The responses in mice towards a novel object depend first of all on the extent of the contrast between the object and the configuration of the background. A novel object placed in a familiar environment released avoidance and burying responses, while the same object placed in a novel environment increased contacts with it and reduced burying. However, even when it was placed in a novel environment, novel object continued to be aversive. These responses also depended on rearing: animals reared in a cage with various objects exhibited a higher number of contacts than mice reared in an "impoverished" environment. Furthermore, burying behaviour can be considered as a species - typical defensive reaction towards a novel object in mice, although these responses have probably no single biological function.