Experiments on the liberation of phosphate from the muscles of the human forearm during vigorous exercise and on the action of sodium phosphate on forearm muscle blood vessels.

1. During vigorous sustained or rhythmic exercise of the forearm muscles, plasma phosphate in the venous effluent from the active muscles increased by about 20%.2. The forearm muscles liberate phosphate during vigorous activity. This confirms observations made by Hilton & Vrbová (1970) on fast muscles in the cat.3. Infusions of sodium phosphate into the brachial artery which raised plasma phosphate in the venous effluent from the resting muscles by 400% had no effect upon the rate of the forearm blood flow.4. These results do not suggest that the liberation of phosphate plays any significant part in mediating the vasodilatation accompanying vigorous exercise of the muscles in the forearm.