The effects of cytokines (interleukin-2, tumor necrosis factor-alpha and interferon-gamma) on the ability of peripheral blood monocytes and alveolar macrophages to produce oxygen radicals were examined by the chemiluminescence assay in patients with lung cancer. Oxygen radical production by peripheral blood monocytes before stimulation with cytokines was lower in the lung cancer group than in healthy controls, suggesting reduced immune function in lung cancer patients. However, the activity in the lung cancer group was elevated to the control level when the monocytes were stimulated by any of the three aforementioned cytokines. Oxygen radical production by alveolar macrophages did not differ significantly between nonstimulated monocytes from lung cancer patients and those from healthy controls. In the lung cancer group, stimulation of the macrophages with any of the three cytokines elevated their ability to produce oxygen radicals to the same extent as in the control group. The results suggest that stimulation of macrophages by interleukin-2, tumor necrosis factor-alpha or interferon-gamma can exert an antitumor action in patients with lung cancer.