The antitumoral effects of interferon (IFN) against renal cell carcinomas (RCC) are considered to consist of a direct tumoricidal activity and an indirect action related to the host immune system. Monitoring to T lymphocytes is an immunological parameter to evaluate the antitumoral effects of IFN. To examine in detail the change of CD8 positive cells reported previously, we analyzed the change of the peripheral blood T lymphocyte subsets using three color flowcytometry during the period of IFN-gamma administration. We administered recombinant interferon gamma (rIFN-gamma) to the patients with renal cell cancer. Eighteen patients received a prophylactic injection of rIFN-gamma (300 x 10(4) units per week) after nephrectomy. Among them three patients developed distant metastases and one had local recurrence after the start of rIF-gamma therapy. We evaluated the immunological change by measurement of the peripheral blood lymphocyte subsets consisting of activated cytotoxic T lymphocytes (ACTL), activated suppressor T lymphocytes (ASTL), activated suppressor-inducer T lymphocytes (AITL), cytotoxic T lymphocytes (CTL), helper T lymphocytes (HTL), and suppressor-inducer T lymphocytes (SITL), from the start of rIFN-gamma injection. We also estimated the natural killer (NK) activity by a cytolytic test at the same points. NK activity consecutively increased throughout the period of administration of rIFN-gamma. We found significant enhancement of ACTL at the sixth month (P < 0.05), ASTL at the third month (P < 0.01) and NK activity at the second week, the first month, the third month and the sixth month (P < 0.01) after the start of rIFN-gamma injection.(ABSTRACT TRUNCATED AT 250 WORDS)