The effects of 12 wk of progressive resistance strength training onin vivo and in vitro immune parameters were evaluated in a controlled study of eight subjects with rheumatoid arthritis (RA), eight healthy young (22-30 yr), and eight healthy elderly (65-80 yr) individuals. Six healthy elderly (65-80 yr) nontraining control subjects were also evaluated to account for seasonal and psychosocial effects. Training subjects exercised at 80% of their one-repetition maximum and performed eight repetitions per set, three sets per session on a twice weekly basis. Peripheral blood mononuclear cell (PBMC) subpopulations, cytokine and prostaglandin (PG) E2 production, proliferative response, and delayed type hypersensitivity (DTH) skin response were measured before and after 12 wk of training. Training did not induce changes in PBMC subsets, interleukin(IL)-1 β, tumor necrosis factor-α (TNF), IL-6, IL-2, or PGE2 production, lymphocyte proliferation, or DTH response in any of the training groups compared with control subjects. These data suggest that 12 wk of high-intensity progressive resistance strength training does not affect immune function in young or elderly healthy individuals or subjects with RA.