Serum levels of carcinoembryonic antigen (CEA), squamous cell carcinoma antigen (SCC) and immunosuppressive acidic protein (IAP) were measured in 37 patients with lung cancers, in 24 with non-cancer pulmonary diseases and in 24 normal controls We evaluated the sensitivity, specificity and accuracy of these three markers alone and combined. The highest specificity was observed for SCC (83.3%) and the highest sensitivity for IAP (94.6%). The best accuracy was obtained with the combined determination of CEA and SCC. In cancer and non-cancer pulmonary diseases the best correlation was observed between CEA and SCC (r = 0.30 in cancer and r = 0.45 in non-cancer pulmonary diseases). Although the IAP test is not specific in the detection of lung cancer, its use may be helpful in monitoring the acute phase reactions that occur very frequently in this malignancy.