Groups of marked wild house mice confined in pens were subjected to repeated live-trapping, to investigate suspected differences in reaction to traps. More males tended to enter traps than females, but the difference between the sexes was not consistently statistically significant. Within each sex, however, some individuals were significantly trap-prone, and some trap-shy. This heterogeneity in response was more pronounced among the females, and there was evidence that it was due to social factors involving the presence of mates. The trap-response of descendants of trap-prone and trap-shy mice suggested that inherent differences might also be involved.