To assess the effects of radiotherapy on immune status, a wide range of assessments have been performed on patients with localized carcinoma of the cervix uteri undergoing and initially responding clinically to radical pelvic radiotherapy. Neutrophil function was essentially unchanged by treatment. Absolute neutrophil and lymphocyte counts fell after treatment and remained depressed 3 and 12 months following treatment. The proportions of T and B cells dropped with treatment but recovered to near-presentation levels during the follow-up period even though absolute counts remained depressed. In vitro tests of cellular immunity were depressed by treatment and remained so 3 and 12 months following treatment whereas skin test responses remained normal throughout the assessments. Inhibitory plasma effects were observed in phytohaemagglutinin lymphocyte transformation studies on 4 untreated patients; at follow-up these effects were not evident. A variable response in immune indices has therefore been observed in patients in remission after treatment of localized carcinoma cervix stressing the importance of assessing several aspects of immune function and implying that persistent depression of certain indices does not adversely affect the host tumor response. In two patients relapsing after apparently good initial response all aspects of immunological assessment (except serum immunoglobulin levels and neutrophil function) deteriorated.