Serum samples from 1185 individuals (blood donors, health care workers, patients on haemodialysis or from other high risk groups or with non-A, non-B [NANB] hepatitis and other liver diseases) were examined for antibody to a recombinant antigen of hepatitis c virus (anti-HCV). A new ABBOTT HCV EIA system was used and a parallel study with ORTHO HCV ELISA was also done for 380 samples to compare the two anti-HCV tests. A confirmatory neutralizing ABBOTT ELISA probe was also performed in 45 cases. Anti-HCV seropositivity was found in 1.60% of accepted healthy blood donors, while among subjects excluded from donation for elevated aminotransferase the rate was 8.95%. In patients on haemodialysis 47.15% anti-HCV prevalence was found, in other high risk group subjects 32.5%. Patients with acute post-transfusion (PT) NANB hepatitis showed 40% prevalence, this rate in chronic PT-NANB was 77.8%. The two ELISA tests revealed 95% agreement in the parallel determinations. Serial dilution studies of anti-HCV positive sera showed that ABBOTT test was of superior sensitivity. The results of the confirmatory test suggest that reactive (positive) samples of low optical density near to the cut-off value require a confirmation with the neutralization test. In conclusion HCV infection in Hungary seems to be a common aetiologic factor in PT-NANB hepatitis and the screening of blood donors for anti-HCV may be useful. However, because of financial difficulties, cost/benefit calculations are recommended before the introduction of this preventive measure.