From September 1996 to May 1997, 187 wild house mice (Mus domesticus) were fitted with radiotransmitters at an agricultural site in the wheatlands of northwestern Victoria, Australia, to examine movements and social organization. Males had slightly larger home-range areas than females. Home-range size was highly variable (0.0002–8.024 ha) but could not be predicted from body size or body condition in males and females, or by whether females were breeding. Mice were site-attached during the breeding season, with extensive intersexual overlap of home ranges but variable intrasexual overlap. Home ranges were significantly larger during the nonbreeding season compared with the breeding season. Evidence existed for exclusive home-range use by females at all densities of mice, low to moderate home-range overlap for males when densities were low and increasing, and an apparent switch to a more gregarious phase in male mice when the breeding season ceased and densities were high. Nonbreeding mice seemed to be nomadic when densities were low, which is consistent with an earlier study of home ranges and social organization of mice on the Darling Downs, Queensland.