Neighbor recognition in the Merriam's kangaroo rat (Dipodomys merriami) was tested in neighbor and nonneighbor pairs of the same and opposite sex in a large enclosure in the field. Mutual tolerance, rather than aggression, occurred in the encounters, and neighbor recognition was more apparent in females than in males. Females tolerated and engaged in nonagonistic contact with familiar males and females; males approached and attempted to contact neighbors and nonneighbors alike. Neighbor recognition is important to both spacing and mating in females. Males' persistent attempts to interact with any conspecific may be important to their mating success.