As a decreased production of Th1 cytokines by stimulated peripheral blood leukocytes has recently been shown in patients with various carcinomas, the present study was performed to determine whether these patients also exhibit a Th1/Th2 imbalance compared to healthy controls. We measured the production of the Th1 cytokines IL-2 and IFN-gamma as well as the Th2 cytokines IL-4, IL-6 and IL-10 in mitogen-stimulated peripheral blood mononuclear cell (PBMC) cultures of patients with urinary bladder carcinomas (n = 47), prostate carcinomas (n = 111) and renal cell carcinomas (n = 67) as compared to 40 age-matched healthy controls. In the PBMC cultures of the tumor patients, the levels of the Th1 cytokines IL-2 and IFN-gamma were lower as compared to the controls. For IFN-gamma, the differences were highly significant and in the patients with renal cell carcinomas it could be shown that the values decreased with increasing tumor mass. In contrast, the levels of the Th2 cytokines IL-4, IL-6 and IL-10 were comparable in the PBMC cultures of tumor patients and controls. From these results, it is concluded that there is only a malfunction in Th1 cells but no switch from a Th1 type to a Th2 type cytokine profile in the PBMCs of cancer patients.