Abstract
The vesicular stomatitis virus cytopathic effect reduction assay is suitable to quantify polyethylene glycol-alpha interferon 2a (PEG-IFN-alpha 2a) and PEG-IFN-alpha 2b. Human serum and ribavirin did not interfere with the assay. This bioassay was successfully used for assaying PEG-IFN-alpha 2a and PEG-IFN-alpha 2b in serum samples from patients undergoing combination therapy.