The present study examined the responsiveness of 19- and 20-day-old C57BL/6J (C) and A/J (A) mouse pups to maternal cues. The C pups were found to spend more time near their C or A foster mother than they did near a virgin female. The A pups showed no such preference. Attempts to increase the motivation of A pups to approach the mother did not produce any preference for maternal cues, However, when the bedding on which odorous substances had been permitted to accumulate for an extended period of time was used as choice stimuli, pups of both lines showed a preference for the bedding of the mother as opposed to that of a virgin female. These results support findings with other rodents of a change in the female's odor during lactation which increases her attractiveness to her pups; and they demonstrate a genetic difference between pups of 2 inbred strains in their approach to maternal cues.