Dose reductions of pegylated interferon alpha and ribavirin may be avoided by using growth factors. This phase II clinical trial assesses the dose, efficacy and safety of darbepoetin alpha and filgrastim for treatment of anaemia and neutropenia associated with combination therapy for hepatitis C virus (HCV). Chronic hepatitis C patients (n = 101) received pegylated interferon alpha-2b (1.5 mug/kg once weekly) and ribavirin (800-1400 mg once daily). Patients with anaemia [haemoglobin (Hb) </= 10.5 g/dL] received darbepoetin alpha (3 mug/kg once every 2 weeks); the dose was titrated to achieve a Hb level of 12.0 g/dL. Patients with neutropenia [absolute neutrophil count (ANC) </= 0.75 x 10(9)/L] received filgrastim with the dose titrated from 150 mug QW to 300 mug thrice weekly to maintain ANC >/= 0.75 x 10(9)/L and <10 x 10(9)/L. During antiviral therapy, 52% of patients required darbepoetin alpha, filgrastim or both. Hb at the time of darbepoetin alpha initiation was 10.2 +/- 0.4 g/dL. After 81 days of darbepoetin alpha, Hb increased by 1.9 +/- 1.0 g/dL to 12.1 +/- 1.1 g/dL (P < 0.0001). Filgrastim resulted in a significant increase in ANC [0.75 +/- 0.16 x 109/L to 8.28 +/- 5.67 x 10(9)/L (P < 0.0001)]. In treatment-naïve patients, 48% achieved sustained virological response (SVR), whereas 27% of patients previously treated with a course of pegylated interferon alpha achieved SVR. Low viral load, nongenotype 1 and treatment with growth factors were independently associated with SVR. Mild and severe anaemia were associated with quality of life impairments. Darbepoetin alpha resulted in an improvement in the Vitality domain of Short Form-36. No significant adverse events were related to growth factors. During anti-HCV therapy, filgrastim improved neutropenia and darbepoetin alpha improved both anaemia and quality of life. Future randomized clinical trials are needed to establish the impact of growth factors in improving sustained virological response.