Abstract: Summary Initial contact with pups of a certain age causes changes in virgin female hamsters' behaviour with pups of another age. This was shown by comparing the behaviour with 5-day-old pups in groups of naive (control) animals and of animals given one previous contact either with 1, 5 or 9-day-old pups. Maternal responses were more intense in the animals previously presented with 1 or 9-day-old pups than in the control animals. Attacking was increased after initial contact with 1-day-old pups and decreased after initial contact with 9-day-old pups. Animals presented twice with the same pattern did not show marked changes in either of the two activities.