The objectives were to determine if a practical method of producing antibodies to PRRSV could be found which would neutralize all strains of the virus. The naturally occurring ambient strains of PRRSV were inoculated into pigs and induced virus neutralizing antibodies to all North American strains of the virus tested. These cross reacting (heterologous) antibodies were protective against the PRRSV when passively injected into pigs. These results confirm previous studies by Osorio and suggest that passive immunization of swine may be a method for reducing PRRSV infection.