Objective:To study the possibilities and limitations of postexposure treatment to prevent the establishment of infection after accidental exposure to HIV.Design and methods:The effect of 2′,3′-dideoxy-3′-hydroxymethyl cytidine (BEA-005) was investigated on acute simian immunodeficiency virus (SIV) and HIV-2 infections in macaques in pre- and postexposure treatment experiments.Results:Postexposure treatment with BEA-005 (3 x 10 mg/kg) for as short as 3 days prevented infection with SIVsmafter intravenous or rectal inoculation. Infection with HIV-2 could also be blocked by postexposure BEA-005 treatment.Conclusion:This study shows that therapeutic intervention can block early systemic and mucosal infections with SIV and HIV-2. Further evaluation is ongoing.