| 1. | Abdominal Abscess (2 recruiting studies) |
| 2. | Abdominal Neoplasms (5 recruiting studies) |
| 3. | Abdominal Pain (3 recruiting studies) |
| 4. | Abetalipoproteinemia (1 recruiting study) |
| 5. | Abnormalities (317 recruiting studies) |
| 6. | Abnormalities, Multiple (14 recruiting studies) |
| 7. | Abnormalities, Radiation-Induced (1 recruiting study) |
| 8. | Abruptio Placentae (1 recruiting study) |
| 9. | Abscess (2 recruiting studies) |
| 10. | Acanthosis Nigricans (1 recruiting study) |
| 11. | Acid-Base Imbalance (4 recruiting studies) |
| 12. | Acidosis (4 recruiting studies) |
| 13. | Acidosis, Lactic (3 recruiting studies) |
| 14. | Acidosis, Respiratory (1 recruiting study) |
| 15. | Acquired Immunodeficiency Syndrome (246 recruiting studies) |
| 16. | Acromegaly (5 recruiting studies) |
| 17. | Actinomycetales Infections (13 recruiting studies) |
| 18. | Acute Idiopathic Polyneuritis (1 recruiting study) |
| 19. | Adenocarcinoma (380 recruiting studies) |
| 20. | Adenocarcinoma, Clear Cell (14 recruiting studies) |
| 21. | Adenocarcinoma, Follicular (4 recruiting studies) |
| 22. | Adenocarcinoma, Mucinous (1 recruiting study) |
| 23. | Adenoma (23 recruiting studies) |
| 24. | Adenoma, Islet Cell (3 recruiting studies) |
| 25. | Adenoviridae Infections (3 recruiting studies) |
| 26. | Adhesions (5 recruiting studies) |
| 27. | Adnexal Diseases (93 recruiting studies) |
| 28. | Adrenal Cortex Diseases (3 recruiting studies) |
| 29. | Adrenal Cortex Neoplasms (3 recruiting studies) |
| 30. | Adrenal Gland Diseases (20 recruiting studies) |
| 31. | Adrenal Gland Hyperfunction (9 recruiting studies) |
| 32. | Adrenal Gland Hypofunction (4 recruiting studies) |
| 33. | Adrenal Gland Neoplasms (5 recruiting studies) |
| 34. | Adrenal Hyperplasia, Congenital (3 recruiting studies) |
| 35. | Adrenoleukodystrophy (3 recruiting studies) |
| 36. | Affective Disorders, Psychotic (27 recruiting studies) |
| 37. | Agammaglobulinemia (1 recruiting study) |
| 38. | Aging, Premature (1 recruiting study) |
| 39. | Agoraphobia (2 recruiting studies) |
| 40. | Agranulocytosis (16 recruiting studies) |
| 41. | AIDS Dementia Complex (2 recruiting studies) |
| 42. | AIDS-Associated Nephropathy (2 recruiting studies) |
| 43. | AIDS-Related Complex (1 recruiting study) |
| 44. | AIDS-Related Opportunistic Infections (3 recruiting studies) |
| 45. | Albinism (2 recruiting studies) |
| 46. | Alcohol Drinking (2 recruiting studies) |
| 47. | Alcohol-Related Disorders (26 recruiting studies) |
| 48. | Alcoholism (28 recruiting studies) |
| 49. | Alkaptonuria (1 recruiting study) |
| 50. | Alopecia (2 recruiting studies) |
| 51. | Alopecia Areata (2 recruiting studies) |
| 52. | alpha 1-Antitrypsin Deficiency (1 recruiting study) |
| 53. | alpha-Mannosidosis (1 recruiting study) |
| 54. | Alzheimer Disease (46 recruiting studies) |
| 55. | Amblyopia (3 recruiting studies) |
| 56. | Amebiasis (1 recruiting study) |
| 57. | Amenorrhea (3 recruiting studies) |
| 58. | Amino Acid Metabolism, Inborn Errors (1 recruiting study) |
| 59. | Amnesia (4 recruiting studies) |
| 60. | Amphetamine-Related Disorders (2 recruiting studies) |
| 61. | Amyloidosis (14 recruiting studies) |
| 62. | Amyotrophic Lateral Sclerosis (6 recruiting studies) |
| 63. | Anemia (121 recruiting studies) |
| 64. | Anemia, Aplastic (18 recruiting studies) |
| 65. | Anemia, Diamond-Blackfan (8 recruiting studies) |
| 66. | Anemia, Hemolytic (32 recruiting studies) |
| 67. | Anemia, Hemolytic, Autoimmune (1 recruiting study) |
| 68. | Anemia, Hemolytic, Congenital (26 recruiting studies) |
| 69. | Anemia, Hypoplastic, Congenital (8 recruiting studies) |
| 70. | Anemia, Refractory (48 recruiting studies) |
| 71. | Anemia, Refractory, with Excess of Blasts (45 recruiting studies) |
| 72. | Anemia, Sickle Cell (23 recruiting studies) |
| 73. | Aneurysm (1 recruiting study) |
| 74. | Angina Pectoris (9 recruiting studies) |
| 75. | Angina, Unstable (3 recruiting studies) |
| 76. | Angiomatosis (7 recruiting studies) |
| 77. | Ankylosis (5 recruiting studies) |
| 78. | Anodontia (1 recruiting study) |
| 79. | Anophthalmos (1 recruiting study) |
| 80. | Anorexia (6 recruiting studies) |
| 81. | Anorexia Nervosa (3 recruiting studies) |
| 82. | Anoxemia (2 recruiting studies) |
| 83. | Anoxia (2 recruiting studies) |
| 84. | Anthrax (2 recruiting studies) |
| 85. | Antiphospholipid Syndrome (1 recruiting study) |
| 86. | Antisocial Personality Disorder (1 recruiting study) |
| 87. | Anus Diseases (7 recruiting studies) |
| 88. | Anus Neoplasms (7 recruiting studies) |
| 89. | Anxiety Disorders (61 recruiting studies) |
| 90. | Anxiety, Separation (1 recruiting study) |
| 91. | Aortic Stenosis, Subvalvular (2 recruiting studies) |
| 92. | Aortic Valve Insufficiency (1 recruiting study) |
| 93. | Aortic Valve Stenosis (2 recruiting studies) |
| 94. | Aphasia (4 recruiting studies) |
| 95. | Apnea (10 recruiting studies) |
| 96. | Apraxia, Ideomotor (2 recruiting studies) |
| 97. | Apraxias (3 recruiting studies) |
| 98. | Arachnoiditis (1 recruiting study) |
| 99. | Arbovirus Infections (3 recruiting studies) |
| 100. | Arnold-Chiari Malformation (2 recruiting studies) |
| 101. | Arrhythmia (9 recruiting studies) |
| 102. | Arrhythmogenic Right Ventricular Dysplasia (1 recruiting study) |
| 103. | Arterial Occlusive Diseases (32 recruiting studies) |
| 104. | Arteriosclerosis (29 recruiting studies) |
| 105. | Arteriovenous Fistula (1 recruiting study) |
| 106. | Arteriovenous Malformations (2 recruiting studies) |
| 107. | Arteritis (1 recruiting study) |
| 108. | Arthralgia (2 recruiting studies) |
| 109. | Arthritis (66 recruiting studies) |
| 110. | Arthritis, Juvenile Rheumatoid (9 recruiting studies) |
| 111. | Arthritis, Psoriatic (3 recruiting studies) |
| 112. | Arthritis, Rheumatoid (39 recruiting studies) |
| 113. | Arthropathy, Neurogenic (1 recruiting study) |
| 114. | Articulation Disorders (2 recruiting studies) |
| 115. | Ascites (2 recruiting studies) |
| 116. | Ascorbic Acid Deficiency (1 recruiting study) |
| 117. | Asperger Syndrome (2 recruiting studies) |
| 118. | Aspergillosis (2 recruiting studies) |
| 119. | Asphyxia (1 recruiting study) |
| 120. | Asthenia (8 recruiting studies) |
| 121. | Asthma (26 recruiting studies) |
| 122. | Astrocytoma (114 recruiting studies) |
| 123. | Ataxia (5 recruiting studies) |
| 124. | Atrial Fibrillation (3 recruiting studies) |
| 125. | Atrophy (15 recruiting studies) |
| 126. | Attention Deficit and Disruptive Behavior Disorders (11 recruiting studies) |
| 127. | Attention Deficit Disorder with Hyperactivity (10 recruiting studies) |
| 128. | Auditory Diseases, Central (1 recruiting study) |
| 129. | Auditory Perceptual Disorders (1 recruiting study) |
| 130. | Autistic Disorder (14 recruiting studies) |
| 131. | Autoimmune Diseases (92 recruiting studies) |
| 132. | Autoimmune Diseases of the Nervous System (23 recruiting studies) |
| 133. | Autoimmune Lymphoproliferative Syndrome (3 recruiting studies) |
| 134. | Autonomic Nervous System Diseases (4 recruiting studies) |
| 135. | Avitaminosis (2 recruiting studies) |
