['The current standard for the determination of sustained virologic response in patients treated for hepatitis C is undetectable hepatitis C virus (HCV) RNA 24 weeks following the completion of therapy. Sensitive molecular tests may permit earlier determination of sustained virologic response following the completion of therapy in end-of-treatment responders.', 'We examined this possibility in 1441 patients, who received 48 weeks of treatment with either standard or pegylated interferon alpha-2a. HCV RNA was determined by polymerase chain reaction assay (Amplicor HCV Monitor vs. 2.0) at baseline and monitored at 4-week intervals throughout the treatment and 24-week post-treatment follow-up periods.', 'End-of-treatment and sustained response were achieved in 624 and 342 patients, respectively. For all treatments, relapse was most frequent at weeks 52 and 56 and became rare following week 60. Only six patients out of 348 patients (2%) became HCV RNA positive between weeks 60 and 72. Analysis of baseline characteristics failed to identify a specific set of parameters associated with early relapse.'] Is twelve weeks of follow-up sufficient for the determination of sustained virologic response in patients treated with interferon alpha for chronic hepatitis C?