Noninvasive markers that accurately follow changes in fibrosis may provide alternatives to liver biopsy for assessment of histological endpoints of antiviral therapy in chronic hepatitis C (CHC). This study compared two commercially available serum marker panels (HCV FibroSURE and FIBROSpect II) during interferon-based therapy. Ninety-five interferon-naïve patients with genotype 1 CHC were enrolled in a phase 2b, active-controlled study of albinterferon alfa-2b/ribavirin for 48 weeks. Proprietary and simple biochemical marker panels were independently evaluated in serum before and during the study. Baseline liver biopsies were evaluated for METAVIR fibrosis by a single pathologist. Index scores were obtained for HCV FibroSURE (n = 84) and FIBROSpect II (n = 95); mean biopsy length: 17.8 +/- 8.0 mm. For detecting fibrosis stages 2-4 (prevalence 23% [22/95] and 21% [18/84]), HCV FibroSURE and FIBROSpect II indicated high sensitivity (1.00 and 0.95, respectively), lower but comparable specificity (0.61 and 0.66, respectively), and a good area under the receiver operating characteristic curve (0.89 and 0.90, respectively). Simple indices had high indeterminate rates (31-40%) at baseline. Patients with a sustained virological response had lower baseline scores than nonresponders, and reduced median percent changes in index scores for HCV FibroSURE (-20.0%vs 2.9%; P = 0.14) and FIBROS Spect II (-6.8%vs 18.4%; P = 0.05). The panels demonstrated comparable performance characteristics for differentiating mild from moderate-severe stage disease in CHC. Lower index scores at baseline that continue to decline likely reflect reduced fibrogenesis activity in patients with successful antiviral responses to therapy.