• This is a report on the history and implications of the collaborative effort that evolved from the 1969 National Institute of Mental Health conference on the psychobiology of depression. The major issues identified at that time were the need to (1) assess relative validities of current systems of nosology and (2) retest critical biological hypotheses concerning the etiology and nature of the depressive disorders. Research was required that would be multidisciplinary and involve clinical settings treating diverse types of depression. The objectives and the nature of the biological and clinical collaborative programs that were designed to address these problems are described. These unique programs, initiated In the early 1970s, currently span research on nosology, genetics, neurochemistry, neuroendocrinology, and psychosocial factors. Although these studies are still in the early stages, they have resulted in significant methodologic developments in diagnosis, descriptive psychopathology, and biological measurements.