Fat determinations, by ether extraction, were made on 205 samples of "sardine" herring (Clupea harengus L.) from the Quoddy region of the Bay of Fundy on the east coast of Canada. The period covered was from 1942 to 1952. The fat content was lowest in April to June and highest from August to November, with few exceptions. It varied between 1.2% and 27.5% of the wet weight of the fish. There was marked variation from year to year. Until sexual maturity was reached, the fatness increased with size. The herring were extremely fat in the winter of 1942–43 and quite poor in the next winter; a remote connection with plankton abundance is discussed. Certain regions are noted for very high fatness. A fungus disease did not greatly affect the fatness of recovering fish.