Investigation of the cellular and humoral immunity in a series of 82 patients with bronchus carcinoma before treatment and in part of them during cytostatic treatment, employing the on the one PHA lymphocyte culture hand and the quantitation of immunoglobulins on the other. In roughly 30% of the cases of untreated bronchus carcinoma reduced immunity was found. This percentage rose during cytostatic treatment, but in several cases it was restored during continuation of the treatment. The median survival of the initial PHA-negative patients was shorter than of the positive reactors. The immunoglobulins were within a normal range in most of the patients before treatment. They changed little during treatment.