The cynomolgus macaques used in this study had originally been kept at the University of Utrecht, where the animals were housed in social groups for up to eight generations. Recently, however, the colony of 135 animals was transferred to the new facilities at the Biomedical Primate Research Centre (BPRC), for the purpose of behavioural studies. The BPRC had access to blood samples drawn during health-checks, and lymphoblastoid cell-lines were established. The origin of the animals was determined by mitochondrial DNA (12S rRNA) analyses (Doxiadis et al. 2003; , and the founder animals appear to have originated either in the Indonesian islands or in continental Malaysia.