AIDS: Specific interactions between HIV and HCV pose concerns for people coinfected with both viruses. PCR testing is recommended to determine the presence of HCV RNA in HIV-positive individuals. Coinfection with HCV is conservatively estimated to occur in about 14 percent of patients with HIV, a rate 10 times higher than that of the general public. Among those who acquired HIV through the use of injection drugs or blood clotting agents, the coinfection with HCV is between 50 and 90 percent. HCV is 10 times more infectious than HIV through these routes. It is rarely transmitted through sexual exposure. The interactions between the diseases, and their similarities and differences, are discussed. Results from studies on treating HCV in coinfected persons are presented. There is a new form of interferon being studied and this is expected to be marketed in the next 2 years.