Provided by the evidences that, in cancer patients, the production of Th 1 cytokines including IL-12, IFN-gamma, and TNF-alpha, is impaired, we asked whether these cytokines can be useful parameters for cancer detection. To the aim 174 patients diagnosed cancer of various organs, and 100 control individuals without cancer were enrolled to the study. We evaluated mitogen-stimulated production of cytokines and induction of Th 1 subset using peripheral blood mononuclear cells in vitro. Th 2 population was measured as the counterpart of Th 1 subset. NK cell activity was also measured. As acquired values did not show the normal distribution we employed a non-parametric test to compare the values between cancer and control. PHA-induced production of IL-12, IFN-gamma and TNF-alpha, in cancer was lower than that in control. Th 1 subset induced in cancer was lower than that in control. We found no difference in Th 2 subset induction between cancer and control. On the other hand, NK cell activity was augmented in cancer patients. When patients were grouped to early stage and advanced stage, both groups showed suppressed production of all three cytokines and suppressed induction of Th 1 cells. Interestingly, none of cytokines nor Th 1 subset differed between the two stages, suggesting that the impaired cytokine production may be a common feature of cancer condition and participate in the etiology of cancer. In contrast, enhanced induction of Th 2 subset was seen in advanced stage compared to early stage, indicating that Th cells might be biased to differentiate to Th 2 cells in advanced stage. From the results IL-12, IFN-gamma, TNF-alpha and Th 1 subset as well as NK activity appear to be promising parameters for cancer detection. Above all, IL-12 and IFN-gamma seem to be the best parameters due to high sensitivity and specificity, and independence from the stage of cancer.