Haptoglobin groups were investigated in 309 patients with primary lung cancer divided by sex, smoking habits and tumor type. Patients with squamous epithelial cancer and oat-cell cancer showed no significant difference from normal controls. Among patients with pulmonary adenocarcinoma the frequency of the Hp 2-2 type was significantly (p less than 0.05) lower compared to the controls, with a corresponding increase of the Hp 1-1 and Hp 2-1 types. This difference was more pronounced (p less than 0.025) among females with pulmonary adenocarcinoma.