BACKGROUND & AIMS: Approximately 75%-85% of patients with chronic hepatitis C virus (HCV) infection do not have a sustained response when treated with interferon (IFN). Limited information exists on the efficacy of retreatment with IFN alone in these patients. The aim of this study was to define the efficacy of IFN retreatment in chronic hepatitis C. METHODS: Ninety-two patients with chronic hepatitis C who had shown transient or no response to recombinant IFN-alpha were randomly retreated with different schedules of lymphoblastoid IFN-alpha and followed up for 12 months after therapy to define biochemical and virological response. RESULTS: None of 26 initial nonresponders obtained a sustained response with retreatment, independent of the schedule used. Thirteen of 66 patients (20%; 95% confidence interval [CI], 10.9-31.3) with transient response during the primary cycle developed a sustained biochemical and virological response when retreated, including 3 of 41 (7%; 95% CI, 1.5-9.9) of those receiving the same schedule and 10 of 25 (40%; 95% CI, 21.1-61.3; P