Tumor markers play an important role in the assessment of patients with some types of malignant tumors. We studied the effects of dialysis and transplantation on the serum levels of five tumor markers; alpha-fetoprotein (AFP), carcino-embryonic antigen (CEA), cancer antigen-125 (CA-125), cancer antigen-19.9 (CA-19.9), and prostate specific antigen (PSA). Serum tumor markers were measured in patients who-had been on dialysis treatment or had a renal transplant for at least one month. Four groups of 30 patients each (hemodialysis, peritoneal dialysis, renal transplant, and normal controls) were studied. Age and sex distribution were comparable between the dialysis and control groups, but the age was significantly younger in the transplant group. Serum AFP and PSA levels were within normal limits in the dialysis and transplant patients. Serum tumor markers, which were raised in the hemodialysis and peritoneal dialysis patients compared to transplant patients and controls, include: CEA (4.5 +/- 2.7 and 5.1 +/- 3.0 vs 1.7 +/- 1.2 and 2.7 +/- 1.2, p < 0.001); CA-125 (41.1 +/- 43.8 and 18.9 +/- 12.7 vs 13.4 +/- 5.7 and 6.1 +/- 4.9, p < 0.001 and p < 0.05); and CA-19.9 (66.0 +/- 60.4 and 66.2 +/- 76.5 vs 20.2 +/- 12.3 and 5.3 +/- 4.5, p < 0.001). Raised CEA, CA-125, and CA-19.9 levels were detected in 37%, 10%, and 53% of peritoneal dialysis patients and 17%, 27%, and 57% of hemodialysis patients. Although the mean serum CEA, CA-125, and CA-19.9 levels were higher in the transplant patients compared to controls.(ABSTRACT TRUNCATED AT 250 WORDS)