A circadian rhythm is demonstrated for salivary CEA in a clinically healthy man who collected unstimulated saliva samples around the clock for 4 days. Its acrophase occurs around 07:00, slightly later than for patients with colon cancer. A circadian rhythm of borderline statistical significance is found for the urinary excretion rate of CEA determined during the same span by this patient. It has an acrophase occurring around 15:00, differing from that of salivary CEA. Although CEA may have only limited value to assess tumor burden, even when determined in blood, rhythm characteristics of tumor markers such as CEA await applications for guiding treatment timing and for detecting earliest chronome alterations not only in the case of an overt cancer but as a feature of predisease and/or disease risk elevation.