Lymphocyte blastogenesis induced by lectins (PHA, Con A, and PWM) was assessed in 27 drug-free patients with unipolar (n = 21) or bipolar (n = 5) depression and 13 normal controls. Fifteen patients were restudied after clinical remission. Symptomatic patients did not differ from controls nor did endogenous and nonendogenous depressions differ in their lymphocyte blastogenesis response to any of the three lectins. However, a significant reduction in lymphocyte blastogenesis with both PHA and Con A stimulation was found following somatic treatment. Cellular immune function appears to be normal in depressed patients, although the somatic therapies are associated with a reduction in this function.