In this randomized, double-blind study, patients' HIV RNA is screened 30 days prior to entry. Patients satisfying enrollment criteria must have been on a stable antiretroviral regimen for 30 days prior to study screening and remain on the same regimen until entry. Patients are stratified based on the screening HIV-1 RNA copy number obtained within 30 days of entry: 5,000 - 50,000 copies/ml versus greater than 50,000 copies/ml. In addition, patients are stratified based on previous antiretroviral use: naive versus experienced. Patients are randomized to one of 2 treatment arms: Arm A - 141W94, plus Zidovudine (ZDV) and Lamivudine (3TC) or Arm B - 141W94, plus ZDV placebo and 3TC placebo.