The serum CEA levels were measured by radioimmunoassay technique in 15 patients with chronic renal failure, who were not treated with hemodialysis, in 39 patients under hemodialysis and in 23 patients who received renal transplantation. The results were compared with those in 65 normal adults and the following results were obtained. 1) Serum CEA concentrations in 65 normal adults were in the range of 1.0 to 4.3 ng/ml with a mean value of 1.6¡¾0.66 ng/ml. 2) Serum CEA concentrations in 15 chronic renal failure patients who were not treated with hemodialysis, were in the range of 0.3 to 8.3 ng/ml with a mean value of 3.6¡¾2.10 ng/m1 which was significantly higher than those of normal controls(P<0.001). 3) Serum CEA concentrations in 39 chronic renal failure patients under hemodialysis were also much higher than normal controls(p<0.001), but not significantly different from those of the patients who were not under hemodialysis(P>0.05). 4) In 23 patients who received renal transplantation, serum CEA levels were significantly higher than normal controls(P<0.001), but not significantly different from those of chronic renal failure patients.