The ability to recoginize conspecifics is a prerequisite for many types of social behaviour, including, for example, parent-offspring relation, mate selection and recognition, territorial defence and dominance coalitions. This ability is of special importance to Hamilton's kin selection hypothesis, which predicts that an individual's behaviour towards a conspecific will depend on the degree of genetic relatedness between them. Although recognition depends on previous experience between individuals in some species, this does not precluded the possibility that recognition could occur in its absence. For example, juveniles who disperse before nonlittermate siblings are born or adult males who do not participate in rearing their young might benefit from recognition abilities that are independent of prior association between the individuals. Here we show that young pigtail macaques prefer to interact with a related over an unrelated monkey in a laboratory test. Because subjects were separated from their dams at birth and reared apart from all other relatives, results suggest that kin recognition can occur in the absence of prior association with relatives.