The functional attributes of minor subpopulations of mouse thymus cells derived by bovine serum albumin density gradient centrifugation, cortisone treatment, or selective depletion by anti-TL or anti-θ treatment have been examined. A subpopulation derived in each fashion contains the cells required to evoke graft-versus-host reactions in neonatal F1 hybrid recipients and to be stimulated by alloantigens in vitro in one-way mixed lymphocyte cultures and by phytohemagglutinin. The functions of this subpopulation are abrogated by treatment with anti-H-2 plus complement and by high concentrations of anti-θ. A tentative ordering of the various thymus cell subpopulations, on the basis of these and other data, is described
