The investigation of the food contents in the stomachs of young fishes was included in the scheme of scientific investigations drawn up and initiated by Professor Herdman for the Lancashire Sea Fisheries Committee nearly thirty years ago. The lengthy series of Annual Reports contain here and there accounts of the observations made on the stomach contents of various Pleuronectidæ captured close inshore, and the pelagic stages of other fishes caught from time to time in the plankton tow-nets. No systematic attempt has, however, been made, in connection with the investigation of the Irish Sea, to determine the food of any particular species of fish during the early part of its life history.Other observers working in other areas, notably Dr. Marie Lebour at Plymouth, have added very much to our knowledge of the early food of young fishes. Dr. Lebour's reports, published in the Journal of the Marine Biological Association, Vols. XI and XII, deal with a very large number of larval and post-larval stages of the more important food fishes caught in the tow-nets and young fish-trawl in Plymouth Sound and beyond.The present report gives an account of the food contained in the stomachs of young plaice (Pleuronectes platessa, Linn.) from a few days after hatching to about five months old. The samples examined in April and May were taken from the spawning pond at Port Erin, Isle of Man, where they had hatched from the pelagic eggs spawned by the adult plaice early in 1921. The later stages examined during May to August represented young plaice hatched in the open sea about the same time as those in the pond, and which had made their way close inshore.