1. Psychiatric evaluation of a group of 29 volunteer research subjects demonstrated the presence of significant psychopathology in 15. In 11 of the 29 subjects psychiatric diagnoses were made.2. There was an inverse relationship in this volunteer group between the presence of psychopathology ( and psychiatric diagnosis) and the extent to which environmental influences contributed to serving as a volunteer.3. The incidence of psychopathology in a subgroup whose volunteer status was largely due to their draft status was 28%; in a second subgroup whose volunteer status conformed with socio-cultural tradition, 59%; in a third subgroup where neither of these factors was operative, 100%. The incidence of psychiatric diagnosis increased in the same direction.4. The volunteer group showed considerable differences in the motivations involved in volunteering, in the ability of its members to accommodate to stress, in defense mechanisms employed, and in the tendency to somaticize anxiety.5. These differences, and the relationship between volunteering and psychopathology, raise a number of questions pertinent to the selection of volunteer groups, and the interpretation of results obtained from them. These questions are discussed.