| 1. | Habits (12 recruiting studies) |
| 2. | Hair Diseases (3 recruiting studies) |
| 3. | Hallucinations (4 recruiting studies) |
| 4. | Hamartoma (4 recruiting studies) |
| 5. | Hamartoma Syndrome, Multiple (1 recruiting study) |
| 6. | Head and Neck Neoplasms (115 recruiting studies) |
| 7. | Head Injuries, Closed (2 recruiting studies) |
| 8. | Headache (2 recruiting studies) |
| 9. | Headache Disorders (2 recruiting studies) |
| 10. | Healthy (254 recruiting studies) |
| 11. | Hearing Disorders (7 recruiting studies) |
| 12. | Hearing Loss (7 recruiting studies) |
| 13. | Hearing Loss, Sensorineural (2 recruiting studies) |
| 14. | Heart Arrest (1 recruiting study) |
| 15. | Heart Block (2 recruiting studies) |
| 16. | Heart Defects, Congenital (9 recruiting studies) |
| 17. | Heart Diseases (110 recruiting studies) |
| 18. | Heart Failure, Congestive (24 recruiting studies) |
| 19. | Heart Septal Defects (1 recruiting study) |
| 20. | Heart Septal Defects, Ventricular (1 recruiting study) |
| 21. | Heart Valve Diseases (4 recruiting studies) |
| 22. | Helicobacter Infections (1 recruiting study) |
| 23. | Helminthiasis (6 recruiting studies) |
| 24. | Hemangioblastoma (3 recruiting studies) |
| 25. | Hemangioma (3 recruiting studies) |
| 26. | Hemangioma, Capillary (2 recruiting studies) |
| 27. | Hemangiopericytoma (11 recruiting studies) |
| 28. | Hemangiosarcoma (8 recruiting studies) |
| 29. | Hematologic Diseases (320 recruiting studies) |
| 30. | Hematologic Neoplasms (31 recruiting studies) |
| 31. | Hemic and Lymphatic Diseases (622 recruiting studies) |
| 32. | Hemiplegia (7 recruiting studies) |
| 33. | Hemochromatosis (2 recruiting studies) |
| 34. | Hemoglobin SC Disease (3 recruiting studies) |
| 35. | Hemoglobinopathies (24 recruiting studies) |
| 36. | Hemoglobinuria (4 recruiting studies) |
| 37. | Hemoglobinuria, Paroxysmal (2 recruiting studies) |
| 38. | Hemolysis (5 recruiting studies) |
| 39. | Hemophilia A (1 recruiting study) |
| 40. | Hemophilia B (3 recruiting studies) |
| 41. | Hemorrhage (16 recruiting studies) |
| 42. | Hemorrhagic Disorders (73 recruiting studies) |
| 43. | Hemorrhagic Fevers, Viral (1 recruiting study) |
| 44. | Hepadnaviridae Infections (8 recruiting studies) |
| 45. | Hepatitis (50 recruiting studies) |
| 46. | Hepatitis A (1 recruiting study) |
| 47. | Hepatitis B (10 recruiting studies) |
| 48. | Hepatitis B, Chronic (5 recruiting studies) |
| 49. | Hepatitis C (33 recruiting studies) |
| 50. | Hepatitis C, Chronic (13 recruiting studies) |
| 51. | Hepatitis D (1 recruiting study) |
| 52. | Hepatitis, Chronic (20 recruiting studies) |
| 53. | Hepatoblastoma (5 recruiting studies) |
| 54. | Hepatorenal Syndrome (1 recruiting study) |
| 55. | Hereditary Central Nervous System Demyelinating Diseases (2 recruiting studies) |
| 56. | Hernia (3 recruiting studies) |
| 57. | Heroin Dependence (1 recruiting study) |
| 58. | Herpes Genitalis (2 recruiting studies) |
| 59. | Herpes Simplex (7 recruiting studies) |
| 60. | Herpes Zoster (2 recruiting studies) |
| 61. | Herpesviridae Infections (43 recruiting studies) |
| 62. | Hip Fractures (2 recruiting studies) |
| 63. | Hip Injuries (2 recruiting studies) |
| 64. | Hippel-Lindau Disease (9 recruiting studies) |
| 65. | Histiocytic Disorders, Malignant (28 recruiting studies) |
| 66. | Histiocytoma, Fibrous (9 recruiting studies) |
| 67. | Histiocytosis (31 recruiting studies) |
| 68. | Histiocytosis, Langerhans-Cell (3 recruiting studies) |
| 69. | HIV Infections (219 recruiting studies) |
| 70. | HIV Seropositivity (5 recruiting studies) |
| 71. | HIV-Associated Lipodystrophy Syndrome (1 recruiting study) |
| 72. | Hodgkin Disease (98 recruiting studies) |
| 73. | Holoprosencephaly (1 recruiting study) |
| 74. | Hookworm Infections (1 recruiting study) |
| 75. | Hot Flashes (13 recruiting studies) |
| 76. | HTLV-I Infections (12 recruiting studies) |
| 77. | Huntington Disease (4 recruiting studies) |
| 78. | Hydatidiform Mole (2 recruiting studies) |
| 79. | Hydrocephalus (1 recruiting study) |
| 80. | Hyperalgesia (2 recruiting studies) |
| 81. | Hyperbilirubinemia (1 recruiting study) |
| 82. | Hypercalcemia (4 recruiting studies) |
| 83. | Hypercholesterolemia (13 recruiting studies) |
| 84. | Hypercholesterolemia, Familial (2 recruiting studies) |
| 85. | Hypereosinophilic Syndrome (29 recruiting studies) |
| 86. | Hyperglycemia (8 recruiting studies) |
| 87. | Hyperhomocysteinemia (1 recruiting study) |
| 88. | Hyperinsulinism (8 recruiting studies) |
| 89. | Hyperkinesis (13 recruiting studies) |
| 90. | Hyperlipidemia (24 recruiting studies) |
| 91. | Hyperlipidemia, Familial Combined (3 recruiting studies) |
| 92. | Hyperlipoproteinemia (3 recruiting studies) |
| 93. | Hyperoxia (1 recruiting study) |
| 94. | Hyperparathyroidism (4 recruiting studies) |
| 95. | Hyperpigmentation (2 recruiting studies) |
| 96. | Hyperpituitarism (5 recruiting studies) |
| 97. | Hyperplasia (11 recruiting studies) |
| 98. | Hypersensitivity (34 recruiting studies) |
| 99. | Hypersensitivity, Delayed (5 recruiting studies) |
| 100. | Hypersensitivity, Immediate (33 recruiting studies) |
| 101. | Hypertension (55 recruiting studies) |
| 102. | Hypertension, Portal (1 recruiting study) |
| 103. | Hypertension, Pulmonary (13 recruiting studies) |
| 104. | Hypertension, Renal (1 recruiting study) |
| 105. | Hypertension, Renovascular (2 recruiting studies) |
| 106. | Hyperthyroidism (2 recruiting studies) |
| 107. | Hypertriglyceridemia (5 recruiting studies) |
| 108. | Hypertrophy (5 recruiting studies) |
| 109. | Hypertrophy, Left Ventricular (1 recruiting study) |
| 110. | Hypoaldosteronism (1 recruiting study) |
| 111. | Hypocalcemia (4 recruiting studies) |
| 112. | Hypoglycemia (2 recruiting studies) |
| 113. | Hypogonadism (7 recruiting studies) |
| 114. | Hypohidrosis (1 recruiting study) |
| 115. | Hypolipoproteinemia (2 recruiting studies) |
| 116. | Hyponatremia (1 recruiting study) |
| 117. | Hypoparathyroidism (3 recruiting studies) |
| 118. | Hypopharyngeal Neoplasms (15 recruiting studies) |
| 119. | Hypophosphatemia (1 recruiting study) |
| 120. | Hypopigmentation (1 recruiting study) |
| 121. | Hypopituitarism (2 recruiting studies) |
| 122. | Hypoplastic Left Heart Syndrome (1 recruiting study) |
| 123. | Hypotension (4 recruiting studies) |
| 124. | Hypotension, Orthostatic (3 recruiting studies) |
| 125. | Hypothalamic Diseases (14 recruiting studies) |
| 126. | Hypothalamic Neoplasms (4 recruiting studies) |
| 127. | Hypothermia (2 recruiting studies) |
| 128. | Hypothyroidism (3 recruiting studies) |
| 129. | Hypotrichosis (2 recruiting studies) |
| 130. | Hypoxia, Brain (5 recruiting studies) |
| 131. | Hypoxia-Ischemia, Brain (5 recruiting studies) |
