Normal volunteers underwent a standard course of treatment to acquire a suntan in a commercial solarium, and tests of immune function were carried out before, on completion, and 2 weeks after completion of radiation exposure. Compared with age and sex matched concurrent controls, the test subjects had reduced skin test responses to dinitrochlorobenzene (DNCB), slightly reduced blood lymphocyte numbers, and changes in the proportion of lymphocyte subpopulations. This included a relative increase in total (OKT3+) T-cell numbers which was attributable to an increase in the OKT8+ suppressor/cytotoxic subset of T cells. OKT4+ helper T cells were reduced and there was a significant decrease in the OKT4/OKT8 ratio. Other changes included a significant increase in suppressor T-cell activity against IgG production in vitro and depression of natural killer cell activity. These changes were still present in some subjects 2 weeks after solarium exposure.