A computerized tube LAI assay was used to determine the antitumor immune response in lung cancer patients. A standardized assay was established by the use of tumor antigen recovered from the spent medium of lung and colon adenocarcinoma cell lines. Furthermore, modulation of the assay by prostaglandin E2 (PGE2) was used to increase its sensitivity. Of 65 patients with epidermoid lung cancer, 34 (52.3%) had a positive nonadherence index (NAI). The NAI was inversely related to tumor burden, with 31 of 44 (70.6%) patients with lung cancer stages I and II and only 3 of 21 (14%.2%) patients with stage III having positive assays (greater than 30%). Addition of PGE2 to the as say increased the overall sensitivity so that a positive NAI was obtained in 88.6% of patients with lung cancer stages I and II, and 88.6% with stage III, respectively. Of 174 individuals from the control group, positive NAI was found in only 9 and 3.8% of patients with chronic obstructive pulmonary disease and normal controls, respectively. These results support previous observations on the specificity and sensitivity of the LAI assay in the diagnosis and study of human cancer.