This Phase I/II study will be conducted in 2 parts each lasting at least 24 weeks. Pharmacokinetics and safety data for part 1, a treatment regimen containing saquinavir and nucleoside antiretrovirals, will be collected for 8 weeks before proceeding to part 2. During the first 8 weeks, pharmacokinetic data will be analyzed to allow dose adjustments for individual patients and to confirm the starting dose estimates for part 2. In addition, safety data will be reviewed to ensure that saquinavir is well tolerated with nucleoside antiretrovirals before it is combined with a second protease inhibitor. In part 2, saquinavir will be combined with nelfinavir, a protease inhibitor recently approved for use in children. The pharmacokinetics and safety profile of these drugs in combination will be determined.