['Serum carcinoembryonic antigen (CEA) is often measured during follow-up of patients surgically treated for colorectal cancer. We determined characteristic findings in serum CEA concentrations or CEA doubling time (DT) depending on the different tumor distributions in colorectal cancer patients.', 'Serum CEA levels were measured monthly until the patients expired in 32 colorectal cancers after operations. CEA DT was based on semilogarithmic plots of time courses of CEA concentrations.', 'In cases who were preoperatively CEA positive, the maximum serum CEA levels for proximal colon, distal colon and rectal cancers were 384.8+/-586.1 ng/mL, 1395.7+/-1954.6 ng/mL and 1343.4+/-1478.3 ng/mL, respectively. The maximum serum CEA level in cases of the proximal colon in preoperative CEA positive patients was lower than that in cases of distal colon or rectum. The average CEA DT on the proximal colon, distal colon and rectal cancers was 71.62+/-43.77 days, 31.07+/-15.98 days and 73.97+/-36.66 days, respectively. The CEA DT with distal colon cancers was also significantly shorter than that with proximal colon or rectal cancers (p<0.05, p<0.02). The CEA DT for lung metastasis was significantly longer than that for liver metastasis, locally or lymph node metastasis or multiple metastases (p<0.02, p<0.02, p<0.001).'] Do distributions in CEA doubling time differ in patients with recurrent colorectal carcinomas?