The effects of uni- and bilateral transections of the medullary pyramids on movements requiring differential use of distal forelimb muscles were studied. The pyramidotomy abolished for more than one year the ability to solve tasks which required flexion and adduction of the digits involved in grasping, e. g. to extract food from narrow horizontal and vertical tubes; unilateral and bilateral pyramidal lesions had comparable effects. In other tasks, involving primarily movements of more proximal muscles, e. g. in retrieving food from behind vertical bars or from between vertical walls, the impairment was both less pronounced and shorter lasting; unilateral pyramidal lesions produced in these movements smaller deficits than bilateral lesions.