Participants will be divided into three groups according to CD4 count levels: > 500 cells/microliter of blood; between 300 and 500 cells/microliter, and < 300 cells/microliter of blood. All participants will be treated with a combination of four antiretroviral drugs: indinavir, zidovudine, lamivudine and nevirapine. (Exceptions to this regimen may be made in certain circumstances for patients who cannot tolerate one of the four drugs.) In addition, they will undergo the following procedures: