Altered cellular immune function has been demonstrated in patients with lung cancer, including decreased numbers of circulating lymphocytes and changes in the percentage of lymphocytes in various functional subsets. We quantitated lymphocyte subsets in 54 patients with lung cancer including patients with limited (stages 1 and 2) nonsmall cell lung cancer (NSCLC, n = 23), advanced (stage 3) NSCLC (n = 16), and small cell cancer (SCLC, n = 15). Serum albumin was decreased in 15 lung cancer patients, and lymphocyte subsets were separately evaluated in these patients. Lymphocyte populations in cancer patients were compared to those of nonsmokers and a smoking patient population. No difference from smokers was noted in patients with limited NSCLC. Patients with SCLC and advanced NSCLC had significantly decreased numbers of T-helper and T-suppressor cells (p less than 0.05). Patients with lung cancer and hypoalbuminemia had the greatest decrease in number of circulating T-helper cells (p less than 0.001). B-lymphocytes were also decreased in patients with advanced NSCLC and patients with hypoalbuminemia (p less than 0.05). A decrease in population of T-lymphocytes subsets is frequent in patients with SCLC, advanced NSCLC, and lung cancer patients with hypoalbuminemia.