Major recent advances in HIV diagnosis include rapid screening serological tests that yield results on the same day of testing, new serological tests that detect infection with a wide variety of different HIV infections including HIV-1 group O and HIV-2, qualitative gene amplification tests (e.g.) that help confirm infection in persons with indeterminate serology, and quantitative gene amplification tests that detect low levels of plasma viremia (>50 virions/ml) and provide prognostic data essential for patient management. Major advances in treatment include the development of drug combinations that completely block HIV replication in a large proportion of adherent previously untreated HIV-infected persons, the demonstration that antiretroviral treatment, under some circumstances, prevents transmission - during pregnancy and following occupational exposure, and the development of sophisticated assays for assessing the drug susceptibility of clinical HIV isolates. Ongoing clinical trials will help clinicians choose the optimal treatment for both previously treated and untreated patients.