The action exerted by the sympathetic system on skeletal muscle is briefly reviewed with regard to the effects induced by the adrenergic mediator on extra-fusal muscle fibre contractility and on muscle spindle receptor organs. In particular, the different responses of slow - and fast - contracting muscles to catecholamine administration and to sympathetic stimulation are reported. Also, the sympathetically--induced effects on muscle spindle afferent activity are discussed on the basis of recent anatomical and functional data suggesting the existence of a direct action exerted by noradrenergic axons on intrafusal muscle fibres. Some of the possible implications of these data are then briefly mentioned.