Patient must be receiving stable nucleoside therapy with at least one agent for >= 4 weeks prior to study day 0. Zidovudine (ZDV), Zidovudine + Dideoxycytidine (ddC), or Zidovudine + Didanosine (ddI) must be used unless prior intolerance precludes ZDV use. Stable use means no change in dose > 50% for any background nucleoside within four weeks prior to study day 0.