Treatment of patients suff ering from chronic hepatitis C with standard pegylated interferon alpha 2a plus ribavirin has limited effi cacy. erapy outcome is dependent on several factors of both the host and virus, including age, sex, stage of fi brosis, viral genotype, viral load, and occurrence of haematological adverse events during chronic hepatitis C treatment. e aim of this study was to determine the relationship between the viral and host factors and the haematological side eff ects of therapy with sustained virological response.Fifty-four patients were treated with combined pegylated interferon alpha 2a plus ribavirin therapy. Hepatitis C virus genotyping, viral load, histopathological liver changes and biochemical parameters were evaluated for each patient before beginning treatment. Each patient's blood count was analysed during each clinical visit.Sustained virological response was achieved in 75,9% of patients. Baseline AST and ALT levels were signifi cantly higher in patients with a poor response to therapy (p<0,05). Other clinical and laboratory parameters did not reach statistical signifi cance. Both responders and non-responders developed anaemia. A decrease in thrombocytes, neutrophils and white blood cells was signifi cantly associated with a sustained response to therapy (p<0,05, p<0,05 and p<0,001, respectively).Sustained virological response was associated with lower baseline AST and ALT values and thrombocytopenia, leucopenia and neutropenia at the end of the treatment. All treated patients developed anaemia.