It is evident that steps can be taken to reduce the risk of contamination risk in primary cell cultures. In practice, different actions are possible: use of virus free animals, use of kidney cells from animals which are less susceptible to virus infections, establishment of veterinary examination and quarantine of animals intended for use, and/or use of diploid or continuous cell lines (use of the cell bank concept/seed stock concept); all reduce the frequency of contamination, Use of captive-bred monkeys versus use of imported wild-caught animals. Besides the advantage of independence from the diminishing wild populations and the sparing of these, it is evident that breeding under controlled conditions led to the production of better quality animals especially in respect of virus infections (Van Steenis et al., 1980) . Van Wezel et al. (1978) could show, by performing serological tests on 18 captive-bred cynomolgous monkeys and 40 imported wild caught parent animals that most of the wild caught animals were positive for antibodies against herpes simplex B, parainfluenza 3, or measles virus, whereas two thirds of the captive bred animals were only positive for antibodies against rotaviruses. Twenty out of 36 imported animals were positive for foamy virus 1 antibodies whereas these antibodies were not observed in the animals bred in captivity (Table I) .