Serum cystatin-C (cys-C), creatinine (Cr), C-reactive protein (CRP) and amyloid A have been shown to provide useful information for renal function following transplantation. In this study, we wanted to evaluate the impact of these parameters as markers of the glomerular filtration rate (GFR) on the third and seventh days of the post-transplantation period. Cys-C was determined by the particle-enhanced immunoturbidimetric assay, and serum amyloid A (SAA) by the sandwich-enzyme immunoassay kit. Cr and CRP concentrations were measured by the Cobas Integra 400 autoanalyser. The patients (n=35) were followed with daily repetitive measurements of serum Cr and urine output per hour, and with Doppler ultrasonography against the risk of rejection. Statistical evaluations were made using the ANOVA and Pearson's test. Serum cys-C and Cr levels on both the 3rd and 7th days after transplantation were lower than those of pretransplantation values (P < 0.001). The Cr/cys-C ratio was decreased on the 3rd day of the post-transplantation period, and kept declining on the 7th day. This ratio was high only in the patient with an acute rejection episode. None of the patients with high pretransplant CRP levels had a rejection episode during a six-month follow-up. SAA concentrations were found to be higher than the pretransplant values in the early post-transplant period. Cys-C had good sensitivity to estimate the renal function in the very early period of transplantation, but its value as a marker of GFR was decreased at the end of first week. As none of the 34 patients had a rejection episode, the observed rise in SAA and CRP levels is not specific to rejection.