Medical authorities have commented that the “compassion” of the physician-investigator for human subjects, together with his professional expertise and other individual qualifications, is more important than, and preferable to social controls, for the protection of subjects' rights and welfare. Data largely from interviews with337research physicians provide a basis for refinement and operationalization of the concept, “compassion,” and permit estimation of the frequency, first, of general concern for human subjects among physician-investigators and, then, of their specific concern for the actual subjects of their own investigations. Some research-related social conditions which tend to engender or activate this concern are specified. Findings of earlier studies, which can lead to an unwarranted conclusion that virtually all research physicians are deeply concerned and involved with their subjects, are thus qualified. The data indicate that physician-investigator “compassion” for subjects is far from universal. In conclusion, the need for social controls, such as peer review, is reaffirmed.