Patients are randomized to receive one of three doses of 1592U89. During this randomized dosing phase, if a patient meets one of the following criteria, he/she is offered open-label 1592U89 (300 mg) plus zidovudine (ZDV) plus lamivudine (3TC) (or other licensed antiretrovirals according to standard practice). Criteria are based on falling CD4 counts (return to baseline on two occasions at least 1 month apart), disease progression (defined as occurrence of a new AIDS-defining event according to CDC classification excluding CD4 counts less than 200 cells/mm3), or lack of virus suppression (defined as less than 0.7log10 reduction in viral load at Week 4 with a repeat value 1 week later, more than 5000 copies/ml HIV RNA at Weeks 12, 16, 20, or 24, or 5000 copies/ml or more anytime after Week 24).