Although AZT and ddI can delay the advancement of HIV disease, the benefit of either of these drugs has proven to be only temporary. d4T, a new nucleoside analog with a favorable toxicity profile and demonstrated activity against HIV, offers an additional therapeutic option. It is reasonably assumed that the benefit of an antiretroviral agent in terms of delaying clinical disease progression is directly related to its ability to achieve and sustain viral suppression; thus, this study measures effects on viral load and CD4 count.