An account has been given of recent work on the chemical nature of war-time swill and on the best methods of using this product so as to ensure the maximum replacement of concentrates, consistent with economical live-weight gains, in the rations of bacon pigs.Three different types of swill have been submitted to investigation: (1) a meat-rich military camp swill, characteristic of the material available during the first 18 months of the war; (2) processed urban swill, commonly known as concentrated swill; and (3) dried, balanced swill. In addition, the results of an investigation into the variation in composition of household and restaurant swill are also given.The different types of swill have been examined from the standpoints of (1) main ingredients, (2) chemical composition, both organic and mineral, (3) digestibility, when fed to bacon pigs, and (4) nutritive value in comparison with mixtures of common pig foods. The keeping qualities of processed urban swill and dried, balanced swill have also been investigated, and attention has been devoted to the problem of the seasonal variations of urban swill in respect of main ingredients, chemical composition and feeding value.