1. A number of local anaesthetics was shown to inhibit rat liver cholesterol esterase activity towards radioactively labelled cholesterol oleate. The anaesthetics inhibited in the order dibucaine greater than chlorpromazine greater than tetracaine greater than benzocaine greater than procaine greater than lidocaine greater than cocaine. 2. The mode of inhibition was seen to be non-competitive with respect to the substrate and is probably independent of any involvement of Ca2+. 3. The inhibition by tetracaine is partially reversed by sodium deoxycholate. However, all ionic and non-ionic detergents studied, sodium deoxycholate, sodium taurocholate, Triton X-100, and cetyltrimethylammonium bromide are capable of inhibiting the rat liver cholesterol esterase in a concentration dependent manner. Only sodium taurocholate stimulates enzymic activity.