We measured the levels of carcinoembryonic antigen (CEA) and the concentrations of neutrophils in serum from healthy smokers. The smokers (n = 1396) had more leukocytes, neutrophils, and lymphocytes than did non-smokers (n = 1123) (leukocytes: 5853 +/- 1627/mm3 vs 4564 +/- 1118/mm3, p < 0.0001; neutrophils: 3533 +/- 1280/mm3 vs 2718 +/- 883/mm3, p < 0.0001; lymphocytes; 1843 +/- 502/mm3 vs 1513 +/- 406/mm3, p < 0.0001). Subjects in whom the levels of CEA was greater than 5.0 ng/ml had significantly higher concentrations of leukocytes, neutrophils and lymphocytes than did those in whom it was 5.0 ng/ml or less (p < 0.0001). Weak correlations were found between serum CEA levels and both the duration of smoking and the Brinkman index. The CEA levels also correlated with daily cigarette consumption (rho = 0.53, p < 0.0001). The concentration of neutrophils in subjects who smoked no more than 20 cigarettes per day or had a CEA level greater than 5.0 ng/ml, or both, was higher than that in subjects who smoked more than 20 cigarettes per day or had a CEA level less than or equal to 5.0 ng/ml, or both (4097 +/- 1325/mm3 vs 3791 +/- 1278/mm3, p < 0.05). These results suggest that in healthy smokers, high serum CEA levels are related to high neutrophil levels.