The effet that being subjected to different environmental situations has in the adult mouse is analysed. Adult mice are placed for that, in groups of twelve mice in cages that contains ramps, catwalks, passages, sleeping boxes and play objects, that were changed in their relative position several times in the week. Oth er mice were placed in groups of four mice in smaller boxes and without these objects. After 60 days in these conditions mice's exploratory behaviour and their learning ability in a complex maze were studied. A significant difference was observed between these two groups, as much in their exploratory behaviour as in the time spent on resolving maze, and the number of mice that resolved it in every one of ten sucesive trials.