Several immunologic parameters have been reported to correlate with the clinicopathologic status of lung cancer patients. However, these studies were based on relatively small numbers of patients and often yielded conflicting results. We prospectively studied cellular immunologic parameters related to age, gender, and stage in lung cancer patients. We obtained pretreatment peripheral blood samples from 287 lung cancer patients. Lymphocyte subsets (percentage of lymphocytes positive for CD3, CD4, CD8, HLA-DR, or representing FcgammaR IIIa-positive T cells), natural killer (NK) cell activity, and lymphoblastogenesis (LB) after stimulation by phytohemagglutinin (PHA) were evaluated. Significant decline was seen in older patients in percentages of cells positive for CD3 or CD4, in the CD4/CD8 ratio and in LB. The percentage of FcgR IIIa-positive T cells increased with age. LB as well as CD4 positivity were significantly greater in women than in men. NK cell activity showed the greatest cytotoxic responses in stage IIIA, with significantly less response in stage IV than in IIIA. Node-negative patients showed higher reactivities for LB and lower positivity for HLA-DR than node-positive patients. Patients with no distant metastases had a higher level of NK cell activity than patients with distant metastases. Immune parameters are variously related to age, gender, and the stage in lung cancer patients, some may prove to be useful predictors of survival.