Rabbit fast hindlimb muscle (tibialis anterior, extensor digitorum longus and peroneal muscles) were stimulated for 14 days, 8 h/day using implanted electrodes, with two different frequencies of stimulation (continuous at 10 Hz or 3 bursts/min at 40 Hz) giving the same total number of stimuli. Both patterns of stimulation resulted in a different pattern of flow and perfusion pressure, with lowered perfusion pressure during contractions in muscles stimulated at 10 Hz and intermittent increase during the peak of tetanic contractions in muscle stimulated at 40 Hz. The arteries supplying the stimulated muscle (anterior tibial artery) were then tested for reactivity to noradrenaline in vitro. Maximal tension developed by control arteries (supplying the contralateral nonstimulated muscles) was 18 ± 1.4 g/mg dry weight in response to 10-5M noradrenaline. Arteries supplying muscle stimulated at 10 Hz showed a significant increase of the maximal response (22 ± 1.5 g/mg) with the same dose. Arteries supplying muscles that had been stimulated at 40 Hz showed decreased response with maximal tension 9.1 ± 1.2 g/mg. Noradrenaline uptake and clearance showed similar values in control vessels and those stimulated at either frequency. Thus, long-term stimulation of skeletal muscles can modify the reactivity of supplying arteries; the response varied with the pattern of contractions and may be explained by a different pattern of flow chang