The effectiveness of passively transferred antibodies directed against the secretory form of herpes simplex virus type 1 (HSV-1) glycoprotein B (gB1-s) was tested in a rabbit model of ocular HSV-1 infection. The animals were passively immunized through the intramuscular injection of a homologous polyclonal anti-gB1-s antiserum at different times from the viral ocular challenge (i.e. at -24, 0, +24 and +48 h from infection). The effects observed in this trial were compared with those obtained in an active immunization trial, in which the animals were vaccinated with gB1-s before the ocular infection with HSV-1 (large variant). The results have shown that passive immunization appears quite effective in prophylactic utilization, whereas it is less effective when performed at 24 or 48 h after inoculation. By contrast, active immunization of rabbits proved to be highly effective both in preventing the development of fatal encephalitis and in reducing the severity of corneal lesions.