Recant data on the relationship of brain rhythms and the simultaneous oscillatory discharge of single units to motor preparation and performance have largely come from monkey and human studies and have failed to converge on a function. However, when these data are viewed in the context of older data from cats and rodents, some consistent patterns begin to emerge. Synchronous oscillatory activity, at any frequency, may be an integrative sensorimotor mechanism for gathering information that can be used to guide subsequent motor actions. There is also considerable evidence that brain rhythms can entrain motor unit activity. It is not clear yet whether the latter influence is a means of organizing muscle phase relationships within motor acts, or is simply a 'test pulse' strategy for checking current muscle conditions. Moreover, although the traditional association of faster brain rhythms with higher levels of arousal remains valid, arousal levels are correlated so tightly with the dynamics of sensorimotor control that it may not be possible to dissociate the two.