Serum levels of CYFRA 21-1(cytokeratin-19 fragment) and ProGRP (pro-gastrin-releasing peptide), the new prognostic markers of lung cancer, were measured by ELISA (enzyme-linked immunoadsorbent assay) in 27 (for CYFRA 21-1; male 13, female 14; age 54+/-17 years) or 22 (for ProGRP; male 9, female 13; age 59+/-18 years) patients with various serum creatinine levels, 42 haemodialysis (HD) patients (male 24, female 18; age 59+/-14 years) and 30 continuous ambulatory peritoneal dialysis (CAPD) patients (male 18, female 12; age 48+/-9 years). All the patients were without clinical and radiological signs of lung cancer. Positive correlations were found between serum creatinine and serum CYFRA 21-1 and ProGRP levels. Serum levels of CYFRA 21-1 were above the cutoff limit (3.5 ng/mL) in 57% of HD patients (mean 4.07+/-1.56 ng/mL) and in 73% of CAPD patients (mean 4.87+/-1.56 ng/mL). Serum levels of ProGRP were above the cutoff limit (46.0 pg/mL) in 90% of HD patients (mean 107.0+/-59.4 pg/mL) and in 93% of CAPD patients (mean 112.4+/-44.5 pg/mL). Our data indicate that evaluation of renal function is essential when the measurement of these tumor markers is to be applied as one of the diagnostic tools of lung cancer.