Allogeneic thymus lobes rendered alymphoid by treatment with deoxyguanosine are not rejected in normal mice despite expression of class I and class II MHC antigens on donor cells. The results presented here show that the injection of as few as 10,000 cells from dendritic cell-enriched populations is followed by the rejection of deoxyguanosine-treated grafts. These findings support the notion that treated thymus grafts do not provoke rejection because they lack dendritic cells, which are destroyed by deoxyguanosine.