Lung metastases from colon adenocarcinoma are often difficult to differentiate from primary lung adenocarcinoma. We studied the diagnostic value of a polyclonal anti-CEA antiserum and two monoclonal anti-CEA antibodies (B18, D14) which define antigens overexpressed in colon carcinoma. Autopsy material from 20 patients with colon carcinoma and lung metastases and 20 specimens from patients with primary lung adenocarcinoma were retrieved, stained, and interpreted without knowledge of the origin of the lung tumor. Colon carcinomas, lung metastases and lung primaries stained positively with polyclonal anti-CEA in 90-100% of cases. D14 stained 75% of colonic metastases and 70% of primary lung adenocarcinomas, whereas 95% of colon primaries were positive. Sixty-five percent of colon primaries and 50% of their metastases were positive with B18, whereas 45% of lung primaries were positive. The frequency of B18 positivity was significantly greater in those colon primaries that were surgically derived (7/9, 78%) compared with their autopsy-derived lung metastases (2/9, 22%) (P less than 0.05). Similarly, D14 staining in surgically derived colon primaries (9/9, 100%) was significantly greater than their autopsy-derived lung metastases (5/9, 56%) (P less than 0.05). In surgical/biopsy-derived tissues 9/9 colonic primaries were D14-positive, whereas only 1 of 6 lung primaries was positive (P = 0.002). We conclude that D14 and polyclonal anti-CEA both stain the majority of colon adenocarcinomas and that changes associated with prolonged fixation may reduce the positivity rate with both B18 and D14 monoclonal antibodies. All three antibodies stain autopsy-derived tissue from primary lung cancer to a significant degree.(ABSTRACT TRUNCATED AT 250 WORDS)