1. A number of local anaesthetics were shown to inhibit the hydrolytic activity of a partially purified lipase from the mold Rhizopus arrhizur towards both triacylglycerol and phospholipid substrates. 2. Irrespective of whether triacylglycerol or phospholipid substrates were used, the inhibition was uncompetitive with respect to the substrate, independent of Ca2+ concentration, but pH dependent. 3. The inhibitory activity of the local anaesthetics studied closely paralleled the anaesthetic potency of the compounds.