Implantation failure in newly inseminated females induced by food deprivation for 48 hr beginning at 10.00 hr on day 4post coitumwas prevented by the presence of the stud male. However, a «familiar» male which had cohabitaded with the female for 7 days or more before pairing with the stud male did not show this protective effect. By contrast, a «familiar» male which had cohabitated with the female for 24 hr during the pericopulatory period provided protection to implantation in food-deprived females, comparable to that given by stud males. The results suggest that exposure to a male, whether the stud male or any other conspecific male, during and immediately after coitus enables the female to memorise the male-originating olfactory cues. This olfactory «memory» induces a luteotrophic effect in the female on re-exposure to the same male after mating. This accounts for the protective effect of the stud male and the «familiar» male on implantation in food-deprived females. The findings also provide additional support to the view that the newly inseminated female mouse is capable of individual identification of males through olfactory cues perceived during the pericopulatory period.