SummaryThe response of forearm skin and muscle vessels to periods of circulatory arrest of 1–10 min. duration has been assessed the technique of superficial and deep venous blood oxygen saturation estimations in 11 experiments on 5 subjects. In every case periods of circulatory arrest were followed by a compictious hyperaemia (rise in oxygen saturation) in both skin and muscle vessels, the response being more marked with longer durations of ischaemia. Corroborative evidence was obtained from 3 experiments in which an increased clearance of a radio‐isotope (NaI131) from forearm skin was observed during reactive hyperaemia. It is concluded that both skin and muscle vessels of the forearm are involved in the phenomenon of reactive hyperaemia.