Reactive hyperaemia in the human forearm has been studied following 5, 10 and 15 min occlusion of the circulation using mercury-in-rubber strain gauges. Following 5 min occlusion the initial high blood flows declined exponentially with a half-life ranging from 14 to 45 s. After 10 and 15 min occlusion the flow pattern is represented by a plateau followed by an exponential of similar time course to the above. Flows did not decay totally along this exponential but deviated onto a second, slower exponential with half-lives ranging from 50 to 560 s. The hyperaemia represented by the area under the second exponential makes a greater contribution to the total flows in non-muscular tissues. It is suggested that this phase of the hyperaemia may be the result of tissue warming during the initial period of high flows.