The aim of this study was to evaluate the prognostic significance of elevated preoperative carcinoembryonic antigen (CEA) levels in cases of resected primary lung cancer. Between 1985 and 1989, 152 patients with tumors and CEA levels above 10 ng/mL underwent operation. One hundred twenty-five of them underwent resection of their tumors and the other 27 underwent exploratory thoracotomy only. Fifty-two percent of cancers were adenocarcinomas and 33% were epidermoid. Forty-two resected tumors were classified as stage I, 29 as stage II, 45 as stage IIIa, 7 as stage IIIb, and 2 as stage IV. The 3-year actuarial survival rate was 54% for patients with stage I tumors, 28% for those with stage II, 18% for those with stage IIIa, 44% for those with stage IIIb, and 0% for those with stage IV tumors. The 5 year actuarial survival was 40% for those with stage I tumors, 28% for those with stage II, 7% for those with stage IIIa, and 0% for those with stage IIIb tumors. Preoperative CEA levels increased from stage I to stage IIIa (p < 0.05). However, based on preoperative CEA levels we were not able to predict resectability, because levels were not significantly different between stage IIIa and exploratory thoracotomy-only groups. Adenocarcinoma was not significantly associated with higher CEA levels than was epidermoid, except in stage IIIa disease (p < 0.05). We found a critical unfavorable level of prognostic significance at 30 ng/mL.(ABSTRACT TRUNCATED AT 250 WORDS)