Since the reports of an international case-control study during the period 1995-1997, further evidence has accumulated supporting the use of postexposure therapy with antiretrovirals. This includes evidence from vertical transmission studies with both zidovudine and nevirapine, and animal model data. Guidelines have been developed and revised for occupational postexposure prophylaxis provision, but there remains considerable debate over postexposure prophylaxis for nonoccupational (predominantly sexual) exposures.