This study was performed to evaiuate the clinical applicability of the reverse t.ranscription polymerase chain reaction (RT-PCR) kit of HCV-RNA using biotinylated and radioiodinat.ed primers. Study subjects were 118 patients with positive anti-HCV. HCV- RNA in patient.s serurn was ext.racted by guanidium thiocyanate method. After first amplification, the product. was reamplified by primers labelled with biotin and I-125. The final amplification product was de- tected by counting t,he radioactivity after incubation in avidin coated tubes. In 51 samples, t.he test was repeated for evaluation of reproducibility. This new method was also compared with conventional RT- PCR rnethods in 34 samples from patients with chronic liver disease. The results were as follows, 1) HCV-RNA was positive in 85(97%)of 88 patients with chronic liver disease, and in 23 (73%) of 30 pat.ients with normal liver function. 2) In comparison with conventional method, HCV-RNA was detected in 32(94%) of 34 patient.s with new method, whereas in 27(79% ) of the same group with conventional method, 3) Repeated test with new rnet.hod in 52 samples demonstrat.ed 82% of concordant result. In conclusion, new rnethod with biotinylated and radioiodinated primers was rnore sensitive than conventional method. However, great care must be taken for quality control because there were considerable interassay variat,ion and possiblity of false positivity and false negativity.