Lurcher mutant mice lose cerebellar granule cells and Purkinje cells. The mutants were compared to normal mice in a beam-walking task. Normal mice were placed on a slippery bridge while lurchers, because of their severe ataxia, were placed on a bridge with the same diameter, but enveloped with surgical tape to improve traction. The performance of both groups improved with repeated trials. In an activity box, lurcher mutants were as active as normal mice, showed normal intrasession habituation, and emerged from a toy object as easily as normal mice. These results indicate that the cerebellar damage in lurchers does not prevent the acquisition of a motor skill task requiring balance in an immobile apparatus. Ataxia was not accompanied by hypoactivity, inhibition or disturbances in intrasession habituation.