To investigate the temporal relationship between CD8(+) lymphocyte phenotypic alterations, the CD4(+) T cell decline, and plasma HIV RNA levels during the natural history of HIV infection, 33 treatment-naive HIV-infected patients with greater than or equal to 400 CD4(+) cells/mu l were studied prospectively for 3 years, During the study period, 20 patients remained untreated, and only 6 received more than 6 months of therapy. A significant relationship was found between changes in plasma HIV RNA and changes in the proportion of CD38(+)CD8(+) cells. Conversely, the number of CD4(+) T cells lost per year was strongly related to the increase in the proportion of CD28(-)CD8(+) T cells. A strong relationship between mean yearly changes in CD4(+) T eel numbers and changes in HIV RNA was also observed. CD4(+) T cell changes were associated with changes in both viral load and CD8(+) T cell activation. These results provide support for the use of both virologic and immunologic parameters for prognosis and management during HIV infection.