Sequential monitoring of non specific immunity has been carried out in 16 patients with squamous cell bronchogenic carcinoma undergoing radical surgery. At the time of diagnosis total lymphocyte counts, T-lymphocyte counts and the blastogenic response of lymphocytes to PHA were only slightly depressed; on the contrary C3c and C4 serum levels were significantly increased (P less than 0.01). Sequential determinations of the immunologic profile at monthly intervals up to the 12th postoperative month showed a transient increase of total lymphocyte and T-lymphocyte levels; the lymphocyte blastogenic response to PHA and also C3c and C4 serum levels progressively decreased. Delayed hypersensitivity response to cutaneous antigens, neutrophil chemotaxis, serum levels of IgG, IgA, IgM and B-lymphocyte counts were constantly found within normal range.