Hepatitis C viral infection (HCV) is the commonest indication for liver transplantation (LTx). Recurrence of HCV is uniform after transplantation. Combination of pegylated interferon (peg-INF) with Ribavirin, which is not without the side effects, has been used as anti HCV treatment. It has been recommended that patients with renal dysfunction should receive lower doses of Ribavirin in order to reduce the incidence of hemolysis. Aim of the present study is to examine the role of measurement of plasma and whole blood concentration of Ribavirin to determine this relationship to hemolysis, renal dysfunction, and treatment response. The left over 34-blood sample drawn for tacrolimus level from 23 post LTx patients (who were on Ribavirin) were used to estimate Ribavirin concentration in plasma (all samples) and blood (17 samples) by HPLC. Patients, clinical history and concurrent medications were evaluated. There was a wide variation in the Ribavirin concentration ranging from 1.8 /l to 122.1 /l with mean plasma concentration of 48.4+ 10.2 /l. There was a close correlation between the plasma and whole blood Ribavirin level (mean plasma level 42.7+ 21.8 /l; mean blood level 37.5 + 17.3 /l.) No correlation was found in the response rate (biochemical, histogical or HCV viral load), hemolysis, renal function or length of Ribavirin treatment on subsequent estimations. However the concentrations were higher when subjects were on antiretroviral agents (5 samples mean 87.3+ 39.4 /l) and lower when patients were on proton pump inhibitors (11 samples mean 29.8+20.3 /l). Despite of the fact that Ribavirin is highly bound to red blood cells, the concentration in whole blood and plasma were similar. Higher concentrations were observed with concurrent use of anti retroviral agents and lower with proton pump inhibiter. The toxicity to the concentration could not be established in this pilot study. It appears that Ribavirin, as a parent compound may not be responsible for therapeutic effect or hemolysis. It is possible that its phosphorelated metabolite of Ribavirin may be determining factor to response rate and toxicity. Further more studies are needed to elucidate the role Ribavirin with peg-INF in recurrent HCV post liver transplantation.