Homing of 51Cr-labelled spleen and lymph node-derived T- and B-cell subpopulations into inflammatory sites in the skin, as well as into lymphoid and non-lymphoid organs, was studied in outbred and inbred guinea-pigs. The early progeny of activated T cells were demonstrated in immunologically-mediated inflammation of the skin, for example a cell-mediated immune reaction and a reversed passive Arthus reaction. In contrast, spleen and lymph node-derived B cells were virtually unable to enter inflammatory sites. Organ-specific homing of T and B cells was detected. The significance of these observations for the interpretation of results of lymphoid cell transfers in guinea-pigs is discussed.