A 20 cm length of the main mesenteric lymph duct in the sheep was cannulated at both ends and measurements were made in both conscious and anaesthetized animals of the ability of the duct to pump saline from an inflow reservoir to an outflow at the same height. Fluid was propelled only when the lymphatic contracted and this was unaffected by movements of the animal round the cage or by fluctuations in abdominal pressure or by respiratory movements. It was confirmed that the mesenteric duct was 'isolated' from the rest of the lymphatic system by closing the inflow tap whereupon fluid propulsion ceased. Raising transmural pressure by varying inflow and outflow by the same amount had the effect of increasing fluid output; this was achieved by an increase in both the frequency and force of lymphatic contractions. Lymphatic frequency of contraction and fluid output increased when the animals were frightened. Intravenous infusions of noradrenaline increased the frequency of lymphatic contraction and increased fluid propulsion, while isoprenaline infusions depressed flow. This preparation demonstrates that it is possible to study the control of lymphatic pumping in conscious sheep without the complication of changing rates of lymph formation.