Social isolation is generally known to promote sexual performances in male mice. We employ here other indices to investigate the positive effects of social isolation on sexual behavior. Mutant staggerer male mice generally do not mate. However some of their reproductive traits can be restored by environmental modifications. We demonstrate that a postpubertal period of social isolation can significantly enhance mutant male sexual behavior. After a period of partial social isolation of one or 2 mo a significantly larger number of mutant males were observed to attempt mounting receptive non mutant C57BL/6 females during a 30 min test encounter. When reproductive success is considered, a larger number of males who were isolated for a period of 2 mo and then allowed to remain with non mutant females were found to sire pups than control (non-isolated) males. The results show that staggerer males isolated for 2 mo can partially overcome the reproductive deficit usually associated with the mutation.