In vitro, telaprevir selects subtype-specific resistance pathways for hepatitis C virus GT-1a and GT-1b, as described to have occurred in patients. In GT-1a, the HCV-796 resistance mutation C316Y has low replication capacity (7%) that can be compensated for by the emergence of the mutation L392F or M414T, resulting in an increase in replication levels of > or = 10-fold.