The incidence of elevated tumor markers without clinical signs of malignant disease was examined in 93 patients between the age of 29 and 79 years and on chronic dialysis for 3-240 months. Tissue polypeptide antigen was found to be elevated in 92.5%, carcinoembryonic antigen in 29.8, and alpha-fetoprotein in 6.5%. High levels of tissue polypeptide antigen were accompanied by high levels of beta 2-microglobulin (p less than 0.005). This indicates that tumor markers, and tissue polypeptide antigen in particular, may be unreliable for monitoring malignant disease in patients on hemodialysis.