The effect of stimulation frequency on intact muscle blood flow was measured by radiolabelled microsphere entrapment. Maximum flow occurred at 4 Hz in both extensor digitorum longus and tibialis anterior (156 ± 13 and 205 ± 24 ml min-1 (100 g)-1, respectively). Regional differences in fibre composition were reflected in the relative flow rates, with functional hyperaemia in the oxidative tibialis anterior core being twice that of the glycolytic cortex at 10 Hz. A consistent difference in flow between legs was noted that may originate from an unequal division of the common iliac artery in rats.