We used the polymerase chain reaction (PCR) to determine the presence of hepatitis C virus (HCV)-RNA in serum samples obtained from 19 patients with leukaemia or severe aplastic anaemia and investigated the correlation between HCV status and the results of liver function tests after bone marrow transplantation. PCR analysis of serum samples obtained before transplant showed that 10 of 18 patients were HCV-RNA-positive; 5 of these patients had developed acute post-transfusion hepatitis 1-11 months before transplant. An additional patient was HCV-RNA-positive on post-transplant day 62. Eight HCV-RNA-positive patients had pre-transplant GPT levels above the upper limit of normal. In these patients the GPT decreased significantly from a median of 104 IU/l (54-822 IU/l) pre-transplant to 23 IU/l (15-56 IU/l) on post-transplant days 8-12. In 9 of 11 HCV-RNA-positive patients, the GPT increased transiently from days 40 to 50 and again increased after day 100. Two of these patients died from hepatic failure; the GPT levels normalised in 3 patients after day 300 but continued to fluctuate in 4 patients. In the remaining 2 HCV-RNA-positive patients, the GPT remained close to the normal range throughout the follow-up period. Three HCV-RNA-positive patients became HCV-RNA-negative after 1-3 years. In these patients, the GPT remained normal for > 3 years after day 300.(ABSTRACT TRUNCATED AT 250 WORDS)