Groups of parentally experienced ♂ and ♀ mice (which had cared for their offspring for 24 days), of sires and dams which had cared for litters (own or fostered) for 1-5 days, and of naive ♂♂ and ♀♀ without breeding experience or contact with pups were tested for their retrieval of test young and discrimination of ultrasonic vocalisation by the young. It was shown that naive ♂♂ and sires that had cared for their pups for 1 day only were non-retrieving. Half the naive ♀♀ and 12 of 15 of dams that had cared for their young for 1 day retrieved test young. Females in the naive and 1-day pup-experience groups did not recognise 50-kiloHertz sounds in preference to 20-kiloHertz ones. Females caring for pups for 5 days and parentally experienced ♂♂ and ♀♀ responded better (P<0.01) to 50-kiloHertz ultrasonic vocalisation than to 20-kiloHertz sounds.