Additional studies looking at the combination of Pegasys and ribavirin included one study comparing two doses and two durations of treatment (24 or 48 weeks) in 1,285 patients, one study comparing 16 and 24 weeks of treatment in 1,469 patients, one study in 514 patients with normal ALT levels, one study in 860 patients who were also infected with HIV, and a final study in 950 patients who did not respond to previous treatment with peginterferon alfa-2b and ribavirin.