Complexation constants of Pb2+and Cd2+nitrates with five crown compounds (18-crown-6, dicyclohexyl-18-crown-6, benzo-15-crown-5, dibenzo-24-crown-8 and 12-crown-4), have been determined by d.c. and a.c. polarographic measurements in aqueous medium using 0.1 M HNO3as supporting electrolyte. The complexes of lead with 18-crown-6 and dicyclohexyl-18-crown-6 are very stable which may be attributed to the partially covalent bonds formed by this metal ion.