The premise that endurance training has beneficial immunologic effects, with encouraging prospects as an adjunct to conventional anti-HIV-1 treatments, is implicit in the current research in exercise immunology. Additionally, the importance of adequate nutrition in maintaining proper immune function in HIV-1 infected individuals is well documented. The current study explored the hypotheses that endurance training would increase absolute numbers of CD4 +, CD+, and NK cells, and improve cardiovascular fitness (VO2max), mood (POMs Depression-Dejection scale) and "psychological outlook" (personality hardiness) in HIV-1 seropositive men. Considering individual dietary habits, it was also hypothesized that consumption of dietary and supplemental antioxidants would increase absolute numbers of the above immune parameters. Forty-six participants were randomized to the control or exercise group. Fitness and psychological assessments were conducted at baseline, 12 weeks, and 24 weeks (endpoint). Diet was assessed with the Willett food frequency questionnaire at baseline and endpoint. An assessment of group equivalency at baseline revealed no significant between-group differences, with the exception of antiretroviral treatment (i.e., longer duration and greater prevalence among exercisers) t (44) = -2.38, p =.02. A repeated-measures ANCOVA, covarying antiretroviral use, revealed a significant main effect due to exercise (p =.01) and a group-by-time interaction (p =.001) for VO2max. Although endurance training increased VO2max, the mean fitness gain of 8% in this sample was smaller than anticipated compared with similar studies in which 15-30% increases have been obtained after exercise training. In the current study, endurance training did not exert significant changes on the immune parameters of interest, affective state, or hardiness. Moreover, correlational analyses revealed no significant relationships between antioxidants and the specified immune parameters for either group. It was concluded that fitness gains may have been attenuated by antiretroviral-induced anemia/mitochondrial DNA suppression, low compliance, and the high baseline fitness levels of several participants. Additionally, exercise-induced mood modulation was less likely because few individuals in this sample had above normal distress levels