The activity of lipoprotein lipase in the vascular bed represents the major pathway by which triglyceride fatty acid is cleared from the plasma and made available to the epripheral tissues. Recent studies on the properties of the enzyme, both solubilized and membrane-bound have provided new information on the regulation of its activity with the major triglyceride-rich lipoprotein substrates. A key role for this enzyme in the regulation of plasma triglyceride levels is indicated from studies of lipase levels in human adipose tissue and in blood plasma obtained after injection of heparin.