To evaluate the diagnostic usefulness of simultaneous determinations of carcinoembryonic antigen (CEA), neuron specific enolase (NSE), chorionic gonadotrophin (HCG) and carbohydrate antigenic determinant 19-9 (CA 19-9), we studied 48 patients with small cell lung carcinoma (SCLC) and 15 with nonmalignant lung disease. The combination of CEA-BAL, NSE-BAL, and NSE-serum taken together with results of bronchoscopy (histologic and cytologic) showed the highest discriminating power between malignant (SCLC) and nonmalignant lung disease. The sensitivity of bronchoscopy alone was 35%. However, when bronchoscopy results were combined with 3 positive markers, the sensitivity increased to 71%, with at least 2 positive markers to 94%, and with at least 1 positive marker to 100%. When both bronchoscopy and all 3 markers were negative, the results showed a negative predictive value of 100%.