Introduction The psychiatric evaluation of "normal" volunteers is an important adjunct to the use of such subjects as "controls" for a variety of biological, pharmacological, and psychological procedures. Reports of other investigators have dealt with the volunteer subject per se,1as well as the methodology involved in selecting control and experimental groups in psychiatric research.2 This paper reports the impressions of a two-year experience in the evaluation of 83 participants, admitted (for periods of two weeks or more) to the National Institute of Mental Health. Emphasis should be placed on the fact that such evaluation is being done routinely on all experimental subjects. In this paper, the observations made by the psychiatrist will be utilized for the purpose of indicating ways in which the characteristics of a volunteer population can be partially predetermined. The following observations will be considered in regard to developing such methods for the selection