Ritonavir and Agenerase Treatment for Patients Who Have Failed Previous Anti-HIV Treatment

Inclusion Criteria Patients may be eligible for this study if they: * Are 18 years of age or older. * Are HIV-positive. * Have a viral load (level of HIV in the body) of more than 1,000 copies/ml. * Have had more than 12 weeks of prior anti-HIV drug treatment. * Have failed a previous anti-HIV treatment containing nelfinavir as the only protease inhibitor. * Are responsive to Agenerase. * Are able to follow study requirements. Exclusion Criteria Patients will not be eligible for this study if they: * Are intolerant to ritonavir (an anti-HIV drug). * Have or have had problems with absorption. * Have liver disease or damage. * Have pancreatic disease or damage. * Have taken any protease inhibitor other than nelfinavir. * Are receiving investigational drugs or devices from another study. * Are pregnant or breast-feeding. * Currently use triazolam, astemizole, ergot medications, cisapride, midazolam, bepridil, rifampin, terfenadine, or pimozide. * Have a bleeding disorder. * Have previously been treated with Agenerase. * Are receiving nonnucleosides.