Four experiments were conducted in aged rhesus monkeys to investigate how physical and psychological stressors influence the lymphocyte cytolytic responses against two target cell lines. An initial analysis of the lytic activity of various cell subsets against K562 and RAJI target cell lines suggested that both CD3+CD8+ and several CD3- subsets were responsible for lysis of the K562 cells. The RAJI cell line, in contrast, was killed primarily by CD3- subsets. To explore the implications of this differential mediation of lysis, cytolytic activity was evaluated after a physical challenge (surgery), a psychological disturbance (social separation), and in vitro incubation of lymphocytes with cortisol. The minor surgical procedure - laparoscopic examination - resulted in a significant decrease in lymphocyte cytolytic responses against both target cells 1 week postsurgery. In contrast, psychological disturbance elicited by changes in social relations caused a dual response, differentially affecting the lysis of either K562 or RAJI cells, dependent upon the type of behavioral reaction. Incubation of lymphocytes with cortisol in vitro indicated that lysis of both targets could be affected by corticosteroids, but the high concentration required (10-6 M) suggested that the in vivo inhibition of cytotoxicity may not have been mediated by adrenocortical activation. Overall, the results highlight the value of utilizing multiple target cell systems in the analysis of cytolytic activity, especially in studies using nonhuman primates.