Summary. Re-treatment with interferon-α alone for chronic hepatitis C nonresponders to interferon-α monotherapy is almost ineffective. This multicentre, randomized, parallel-group, dose-finding study evaluated the efficacy of interferon-β-1a in the treatment of chronic hepatitis C patients unresponsive to interferon-α. A total of 267 patients were randomized to one of four groups: subcutaneous interferon-β-1a 12 MIU (44 μg) or 24 MIU (88 μg) administered three times weekly or daily. Patients were treated for 48 weeks and then followed up for an additional 24 weeks. There was a trend towards a dose–response relationship regarding virological [loss of detectable serum hepatitis C virus (HCV) RNA] and biochemical response (normalization of serum alanine aminotransferase). Overall, 22 patients (8.3%) had a virological response at the end of treatment; nine patients (3.4%) had a sustained virological response (SVR). Strikingly, 21.7% (5/23) of Chinese patients achieved SVR. Univariate analysis revealed that race was the only variable related to SVR [odds ratio (OR) 16.6; 95% CI 4.1–67.3; P < 0.0001]. Multiple logistic regression analysis also confirmed that more Chinese patients achieved SVR than non-Chinese patients (OR 12.3; 95% CI 2.6–59.3; P = 0.0017). In addition, complete clearance of HCV-RNA occurred earlier in Chinese than in non-Chinese responders (median 2 vs 30 weeks; P = 0.020). Thirty-six patients were withdrawn from treatment because of adverse events. Most adverse events were mild or moderate in severity. In conclusion, interferon-β-1a provided considerable clinical benefit in Chinese patients with chronic hepatitis C unresponsive to interferon-α. The evaluation of interferon-β-1a in this setting is progressing.