Use of kidney cells from animals, which are less susceptible for virus infections. One way to reduce the contamination by human pathogenic virus is to change the species of the animal as donor of the primary cells. Shah and Nathanson (1976) proposed that new world spider monkeys should be used instead of the rhesus monkeys or macaques because SV40 does not readily multiply in cells from spider monkeys. On the other hand, macaque monkeys can be infected with Herpes simiae or B viruses, which are highly pathogenic for humans. The replacement of the macaques as donors by African Green Monkeys, which are not susceptible to infection by herpes simiae virus, would be the best precaution in this case (Minor, 1996) .