Groups of 20 to 50 foragers from two different honeybee colonies were trained, in turn, to syrup in two dishes 1 to 3 ft. apart. Both groups were then allowed to visit their dish at the same time, and newcomers were then found to be preferentially attracted to the dish visited by members of their own colony. This preferential attraction was shown to be a consequence of distinguishable odours emitted by the workers. These odours were not genetically inherited but were derived from metabolic differences between their colonies. These differences were produced by changes in food supply, and probably also through differences in breeding rhythms. They would develop between queenless halves of colonies. Uniform and distinguishable colony odours are a consequence of widespread food transmission among the foragers of each colony. The role of olfactory recognition in the social life of the bee is discussed.