Lymphocyte subsets home in a particular manner depending on their class, state of activation and 'allegiance' to certain tissues. Naive lymphocytes home preferentially through lymphoid tissues, whereas effector and memory cells home preferentially through non-lymphoid tissues and exist as phenotypically distinct subsets with preferential localization to gut, skin or other tissues. These migration pathways, which correlate with different functional properties of lymphocyte subsets, increase the efficiency of the immune system.