1. The blood flow in rabbit gastrocnemius, as measured by photoelectric drop-counter, increased when the muscle was vibrated at frequencies of 22–62 Hz. 2. Blood flow increased rapidly within 1–2 s of the start of vibration, and lasted for the whole time vibration was applied. 3. The increase in blood flow was negatively correlated with the initial blood flow, being greater with lower flows. 4. The magnitude of increase was similar in both innervated and acutely denervated muscles. 5. The arterial blood pressure did not change apart from a very brief fall at the beginning of vibration. Venous pressure rose and, consequently, the perfusion pressure was lower. The increase in blood flow thus indicates a considerable dilatation in the resistance vessels of skeletal muscle.