| 1. | Macular Degeneration (18 recruiting studies) |
| 2. | Macular Edema, Cystoid (1 recruiting study) |
| 3. | Malabsorption Syndromes (3 recruiting studies) |
| 4. | Malaria (7 recruiting studies) |
| 5. | Malaria, Falciparum (5 recruiting studies) |
| 6. | Malignant Carcinoid Syndrome (6 recruiting studies) |
| 7. | Malignant Fibrous Histiocytoma (9 recruiting studies) |
| 8. | Malnutrition (3 recruiting studies) |
| 9. | Malocclusion (1 recruiting study) |
| 10. | Mandibular Diseases (5 recruiting studies) |
| 11. | Mannosidase Deficiency Diseases (1 recruiting study) |
| 12. | Mansonelliasis (1 recruiting study) |
| 13. | Marijuana Abuse (2 recruiting studies) |
| 14. | Mastigophora Infections (2 recruiting studies) |
| 15. | Mastocytosis (5 recruiting studies) |
| 16. | Mastocytosis, Systemic (1 recruiting study) |
| 17. | Maxillofacial Abnormalities (2 recruiting studies) |
| 18. | Meconium Aspiration (1 recruiting study) |
| 19. | Median Neuropathy (2 recruiting studies) |
| 20. | Mediastinal Diseases (2 recruiting studies) |
| 21. | Mediastinal Neoplasms (2 recruiting studies) |
| 22. | Medullary Thyroid Carcinoma (3 recruiting studies) |
| 23. | Medulloblastoma (37 recruiting studies) |
| 24. | Melanoma (102 recruiting studies) |
| 25. | Melanosis (2 recruiting studies) |
| 26. | MELAS Syndrome (1 recruiting study) |
| 27. | Memory Disorders (7 recruiting studies) |
| 28. | Meningeal Neoplasms (12 recruiting studies) |
| 29. | Meningioma (22 recruiting studies) |
| 30. | Meningitis (5 recruiting studies) |
| 31. | Meningoencephalitis (1 recruiting study) |
| 32. | Meningomyelocele (1 recruiting study) |
| 33. | Menkes Kinky Hair Syndrome (1 recruiting study) |
| 34. | Menopause (18 recruiting studies) |
| 35. | Menstruation Disturbances (5 recruiting studies) |
| 36. | Mental Disorders (400 recruiting studies) |
| 37. | Mental Disorders Diagnosed in Childhood (45 recruiting studies) |
| 38. | Mental Retardation (14 recruiting studies) |
| 39. | Mental Retardation, X-Linked (5 recruiting studies) |
| 40. | Mercury Poisoning (1 recruiting study) |
| 41. | Mesenchymoma (7 recruiting studies) |
| 42. | Mesothelioma (21 recruiting studies) |
| 43. | Metabolic Diseases (183 recruiting studies) |
| 44. | Metabolism, Inborn Errors (53 recruiting studies) |
| 45. | Metaplasia (4 recruiting studies) |
| 46. | Methylmalonic Acidemia (1 recruiting study) |
| 47. | Microphthalmos (1 recruiting study) |
| 48. | Migraine (3 recruiting studies) |
| 49. | Mitochondrial Diseases (4 recruiting studies) |
| 50. | Mitochondrial Encephalomyopathies (1 recruiting study) |
| 51. | Mitochondrial Myopathies (1 recruiting study) |
| 52. | Mitral Valve Insufficiency (2 recruiting studies) |
| 53. | Mixed Connective Tissue Disease (1 recruiting study) |
| 54. | Monoclonal Gammopathy of Undetermined Significance (3 recruiting studies) |
| 55. | Mononeuropathies (4 recruiting studies) |
| 56. | Mood Disorders (88 recruiting studies) |
| 57. | Motor Neuron Disease (16 recruiting studies) |
| 58. | Mouth Abnormalities (2 recruiting studies) |
| 59. | Mouth Diseases (42 recruiting studies) |
| 60. | Mouth Neoplasms (26 recruiting studies) |
| 61. | Movement Disorders (66 recruiting studies) |
| 62. | Mucinoses (2 recruiting studies) |
| 63. | Mucocutaneous Lymph Node Syndrome (1 recruiting study) |
| 64. | Mucolipidoses (1 recruiting study) |
| 65. | Mucopolysaccharidoses (3 recruiting studies) |
| 66. | Mucopolysaccharidosis I (2 recruiting studies) |
| 67. | Mucopolysaccharidosis IV (9 recruiting studies) |
| 68. | Mucopolysaccharidosis VI (2 recruiting studies) |
| 69. | Multiple Endocrine Neoplasia (2 recruiting studies) |
| 70. | Multiple Myeloma (100 recruiting studies) |
| 71. | Multiple Organ Failure (6 recruiting studies) |
| 72. | Multiple Sclerosis (19 recruiting studies) |
| 73. | Multiple Sclerosis, Chronic Progressive (2 recruiting studies) |
| 74. | Multiple Sclerosis, Relapsing-Remitting (4 recruiting studies) |
| 75. | Multiple System Atrophy (3 recruiting studies) |
| 76. | Muscle Cramp (7 recruiting studies) |
| 77. | Muscle Hypertonia (1 recruiting study) |
| 78. | Muscle Hypotonia (1 recruiting study) |
| 79. | Muscle Neoplasms (7 recruiting studies) |
| 80. | Muscle Rigidity (1 recruiting study) |
| 81. | Muscle Spasticity (4 recruiting studies) |
| 82. | Muscle Weakness (4 recruiting studies) |
| 83. | Muscular Atrophy (4 recruiting studies) |
| 84. | Muscular Atrophy, Spinal (3 recruiting studies) |
| 85. | Muscular Diseases (47 recruiting studies) |
| 86. | Muscular Disorders, Atrophic (7 recruiting studies) |
| 87. | Muscular Dystrophies (5 recruiting studies) |
| 88. | Muscular Dystrophy, Duchenne (2 recruiting studies) |
| 89. | Muscular Dystrophy, Facioscapulohumeral (1 recruiting study) |
| 90. | Musculoskeletal Abnormalities (6 recruiting studies) |
| 91. | Musculoskeletal Diseases (195 recruiting studies) |
| 92. | Mutism (1 recruiting study) |
| 93. | Myasthenia Gravis (1 recruiting study) |
| 94. | Mycobacterium Infections (13 recruiting studies) |
| 95. | Mycobacterium Infections, Atypical (1 recruiting study) |
| 96. | Mycoses (133 recruiting studies) |
| 97. | Mycosis Fungoides (54 recruiting studies) |
| 98. | Myelitis (8 recruiting studies) |
| 99. | Myelodysplasia (172 recruiting studies) |
| 100. | Myelodysplastic Syndromes (172 recruiting studies) |
| 101. | Myelofibrosis (31 recruiting studies) |
| 102. | Myeloid Metaplasia (2 recruiting studies) |
| 103. | Myeloproliferative Disorders (93 recruiting studies) |
| 104. | Myocardial Diseases (6 recruiting studies) |
| 105. | Myocardial Infarction (23 recruiting studies) |
| 106. | Myocardial Ischemia (54 recruiting studies) |
| 107. | Myocarditis (2 recruiting studies) |
| 108. | Myoclonus (3 recruiting studies) |
| 109. | Myofascial Pain Syndromes (10 recruiting studies) |
| 110. | Myopia (1 recruiting study) |
| 111. | Myosarcoma (20 recruiting studies) |
| 112. | Myositis (11 recruiting studies) |
| 113. | Myositis, Inclusion Body (3 recruiting studies) |
| 114. | Myotonic Disorders (1 recruiting study) |
| 115. | Myotonic Dystrophy (1 recruiting study) |
