1. Six male subjects performed simulataneous static (hand-grip) and rhythmic (bicycle ergometer) exercises while their respiratory responses were measured. 2. Oxygen consumption increased with the intensity of rhythmic work load, with a modest additional oxygen consumption accompanying the addition of static effort during the rhythmic exercise. 3. Minute ventilation (VE) increased directly with rhythmic exercise, but increased disproportionately to the metabolic need when static effort was added. The mean increment of VE elicited by the static exercise influence was nearly constant at 20 l/min, regardless of the rhythmic load present. 4. Possible reflex mechanisms which result in disruption of the normally well-matched ventilation and metabolic oxygen demands whenever static effort is present are discussed.