We studied the effect of hepatitis C virus coinfection on T cell subpopulations in HIV-infected patients receiving antiretroviral therapy. Coinfection with hepatitis C virus was followed by a decrease in the number of naive CD4+ T cells and an increase in the count of central CD8+ memory T cells in these patients. Hepatitis C virus had no effect on the number of CD4+ memory T cells (main target for HIV). This can explain the absence of strong negative effect of hepatitis C virus on the course of HIV infection