Boceprevir is an HCV NS3 (non-structural protein 3) serine protease inhibitor being developed by Schering-Plough Corp as a capsule formulation. In pharmacokinetic studies, boceprevir was adequately absorbed, with the most effective mode of administration appearing to be a three-times-daily regimen. In phase I clinical trials, monotherapy with boceprevir led to a distinct viral load reduction. In phase Ib combination trials of boceprevir with PEGylated IFNalpha2b and ribavirin, the reduction in viral replication was further increased. Early data reported from phase II clinical trials have been promising, suggesting a rapid early HCV-RNA reduction. Phase III trials for the drug began in 2008. Results available to date have demonstrated the compound to be well tolerated, with adverse events that were within the range of current standard-of-care therapy. Thus, boceprevir may have the potential to increase sustained virological response rates and possibly also to shorten duration of therapy; data from ongoing clinical trials are awaited.