Iron-loss measurements on grain-oriented silicon-iron transformer steel show that the anomalous loss under normal transformer core working conditions now amounts to about one half of the total iron loss. Experimental data have been obtained for five different directions in the sheet. The results show that the theory, as at present expounded, that anomalous losses arise from eddy currents at moving domain boundaries, is not adequate to account for the high magnitude of these losses. The origin of anomalous losses seems, therefore, to be still in doubt.