OBJECTIVES: The Brazilian government has published guidance for the use of peguilated interferons for the treatment of CHC in adults. However, there is no differentiation between the drugs either concerning efficacy or cost effectiveness. We used a previously published Brazilian Markov model to compare these two drugs in terms of cost utility. METHODS: The Brazilian Markov model describes the clinical history of CHC in which cohorts of hepatitis C virus (HCV) patients receive peginterferon alfa 2b or peginterferon alfa 2a for either 48 or 24 weeks according to genotype and liver histology and were followed for their life expected life time. The reference patient was a 30-year-old male with CHC without cirrhosis. The SVRs to PEG2b and PEG2a were 48% and 46% for HCV genotype 1 and 88% and 76% for non-1, respectively. Quality of life for each health state was based on literature. Costs for each health state was based on three Delphi panels, one with hepatologists, one with intensivists and another with oncologists. Costs in 2005 reais and benefits were discounted at 3%. RESULTS: In HCV genotype 1 PEG2b increases life expectancy (LY) by 0.07 years and quality adjusted life expectancy (QALY) by 0.13 years compared to PEG2a. In these patients PEG2b is less costly than PEG2a (R$ 3.763,33 difference). In HCV non-genotype 1 patients PEG2b increases LY by 0.44 and QALY by 0.76. Also, in HCV non-genotype 1 patients PEG2b was less costly than PEG2a (R$ 6.371,04 difference). CONCLUSIONS: Peguinterferon alfa 2b is dominant, in pharmacoeconomics terms, in comparison to PEG2a for the treatment of HCV adult patients, in Brazil.