Two studies examining the interactions between adults and young guinea pigs were reported. Both studies were of the same design, and consisted of a series of time-sampling observations of the social behaviour of a litter of young guinea pigs and their mother, housed in a single cage with either an adult virgin female (in the first experimental condition) or an adult male (in the second experimental condition). Daily observations were also made, after the infant animals had been removed from their cage for a few hours each day, on reintroducing them to the two adult guinea pigs. It was found that although infant animals interacted with the non-lactating adult, in particular the adult male, these social interactions tended to be unlike those between the young and their mother. Responses such as suckling and all other physical contact were directed predominantly to the mother, whereas near responses (remaining near an adult but not in contact with it) occurred more often in relation to the other adult. It was found that infants could distinguish the adults by distal cues, and in the reintroduction study the mother was preferred to the other cohabitant adult on all behavioural measures. It was suggested that infant animals may recognise classes of adults (for example, male, lactating female, non-lactating female) at a distance, but individuals may only be distinguished by proximal cues, since an earlier study has found that infants did not distinguish their mother from another lactating female at a distance. In general, no sex differences in behaviour were found in the infant animals. It was concluded that the infant guinea pig plays a somewhat larger part in enforcing mother-young interactions than was previously thought, and it was suggested that observations on a colony of guinea pigs would be of great value in further investigating this whole area of research.