This Phase I/II trial is being conducted with a new anti-HIV drug called 1592U89. This is a preliminary trial of this compound which has been shown in-vitro to have anti-HIV activity because it inhibits the virus reverse transcriptase (RT). This activity has been demonstrated to be synergistic in combination with Retrovir (AZT, zidovudine), didanosine (ddl) and zalcitabine (ddC). In addition, resistance against 1592U89 has ben shown to be caused by a mutation in the RT that suppresses AZT resistance. This premliminary information, combined with its favorable pharmacological profile, including penetration into the brain, makes 1592U89 a good candidate for further clinical development. This is a Phase I/II study being conducted to evaluate safety, tolerance and pharmacokinetics of 1592U89 along and in combination with zidovudine. This trial is designed to provide information on the clinical activity of this drug as measured by its effects of virologic and immunologic markers. These will include viral load and CD4 counts, viral SI/NSI phenotype, drug resistance, and pharmacokinetc assays will also be performed. In addition, patients will be evaluated clinically at regular intervals. The primary endpoints are safety, tolerance and kinetics of 1592U89. Also, preliminary antiretroviral activity will be studied. HIV-infected patients with CD4 cells between 200 and 500 who are otherwise stable clinically will be studied. Patients will be recruited from private physicians. There is no remuneration currently in place for participation in this study. Up to 15 patients will be studied at MGH.