Experiments were designed to assess whether cryopreserved PBL could be used to monitor the immunological effects of IFN-alpha therapy in renal cell carcinoma (RCC) patients. It was found that programmed freezing and thawing of peripheral blood lymphocytes (PBL) from normal blood donors did not substantially change lymphocyte subset proportions and that cryopreserved PBL were able to proliferate in response to IL-2. It was also possible to activate the cytolytic activity of frozen PBL, and the frozen leukocytes did not lose their ability to secrete IFN-gamma after PHA activation. We have used these findings to investigate the immunological effects of IFN-alpha therapy in RCC patients. Cryopreservation of PBL samples collected from various patients over a period of 9-14 months enabled us to compare the in vitro reactivity of PBL from individual RCC patients repeatedly and under standard conditions. It was found that IL-2 induced proliferative responses of PBL from IFN-alpha non-responders, collected prior to IFN-alpha therapy, were significantly decreased as compared to those from normal blood donors. The proliferative responses of PBL from IFN-alpha responders, collected prior to IFN-alpha therapy, did not substantially differ from normal controls. Culture of PBL from IFN-alpha responders for 3 days in IFN-alpha-containing medium increased their lytic activity towards RCC targets, whereas no such increase was observed with non-RCC targets or using PBL from IFN-alpha non-responders or PBL from normal-blood donors. Enzyme-linked immunospot (ELISPOT) assays performed with cryopreserved lymphocytes from IFN-alpha non-responding RCC patients, collected prior to IFN-alpha therapy, revealed a substantially decreased ability to secrete IFN-gamma, as compared to IFN-gamma secretion of PBL from IFN-alpha responders or normal blood donors.