Peripheral blood T lymphocyte subsets were quantitated by monoclonal antibodies in 91 patients with urologic malignancies as well as eight age-matched controls. In general, the presence of cancer and increasing stage were associated with a relative decrease in helper and an increase in suppressor T-cell activity as well as a decreased T4/T8 cell ratio. Therapy in the form of androgen depletion reversed these trends and restored helper and suppressor levels as well as the T4/T8 ratio to control values. In a small subset of sixteen patients surgery had only modest immediate (prostate) and long term (kidney) effects on these parameters.