CEA serum levels were sampled from 15 patients with lung carcinoma, 12 patients with colon carcinoma, and 5 patients with gastric carcinoma before and after radical excision of the malignancy. In addition, TPA serum levels were measured in 7 patients with lung carcinoma and CA 19.9 serum levels in 9 patients with colon carcinoma, before and after curative surgery. Irrespective of the primary malignancy, a CEA half-life of approximately 3 days was calculated. The normalization time was related to the preoperative level of the marker, being longer when the preoperative CEA level was > 20 ng/ml. The TPA half-life was slightly longer than 1 day, ranging from less than 1 day to more than 3 days, with a normalization time of about 20 days. The CA 19.9 half-life was slightly longer than 1 day with variations from less than 1 day to about 3 days. Many factors, especially associated inflammatory processes and hepatic clearance imbalances, may influence marker kinetics in the postoperative period. A correct evaluation of the clinical significance of tumor marker half-life after radical surgery will require a larger number of patients as well as careful and prolonged follow-up.