BACKGROUND: Several small studies have reported a lower response rate to interferon alfa among black patients with chronic hepatitis C infection than among white patients. The increased prevalence of infection with hepatitis C virus (HCV) genotype 1, which has a lower response rate than other genotypes, has been suggested as the cause. METHODS: We treated 100 black patients and 100 non-Hispanic white patients with chronic hepatitis C with peginterferon alfa-2b and ribavirin for 48 weeks. Enrollment was controlled so that the two groups had similar proportions of patients with genotype 1 infection. The primary end point was a sustained virologic response, which was defined as a negative test for serum HCV RNA six months after the completion of therapy. RESULTS: In both cohorts, 98 percent of patients had genotype 1 infection. The rate of sustained virologic response was higher among non-Hispanic white patients than among black patients (52 percent vs.19 percent, P<0.001). The black patients also had significantly lower rates of virologic response at 12 weeks and at the end of treatment. Multivariable analyses examining sociodemographic and clinical characteristics found that black race was the only variable significantly associated with the difference in response rate. CONCLUSIONS: Black patients with chronic hepatitis C have a lower rate of response to treatment with peginterferon alfa-2b and ribavirin than non-Hispanic white patients, a difference that is not explained by differences in the viral genotype. Copyright 2004 Massachusetts Medical Society