The following tumor markers, AFP, CEA, CA 19-9, CA-125 and CA 15-3 were studied in 50 healthy volunteers (group A), in 23 patients on chronic hemodialysis (group B) and in 30 successfully transplanted individuals (group C) who did not present any clinical symptoms or signs of neoplasia. The levels of AFP, CEA and CA 15-3 were significantly higher in group B when compared to groups A and C. The levels of CA 19-9 and CA-125 did not differ significantly among the three groups. Transplanted individuals (group C) presented significantly lower levels of CEA and AFP and higher levels of CA 15-3 when compared to group B patients. The levels of all markers were not influenced by sex or time on dialysis. It is concluded that: (1) CA 19-9 and CA-125 can be considered as reliable tumor markers in patients undergoing hemodialysis or kidney transplantation. (2) The elevation of CEA and AFP levels in hemodialysis and their decline to normal levels found in the group of successfully transplanted individuals, suggest a possible active role of functioning renal tissue in their clearance. (3) The etiology of CA 15.3 elevation following successful kidney transplantation remains obscure and requires further evaluation.