Allogenic peripheral blood stem cells (PBSC) were used for graft failure after BMT in two patients. These PBSC were mobilized by G-CSF in the same donors, harvested and given without reconditioning to the patients. In one patient, PBSC with a very high T cell number were given unprocessed, in the other patient, CD34+ cells were positively enriched due to a 2-antigen difference. None of the patients had hyperacute GVHD. Trilineage engraftment was seen after 13 days. Acute GVHD grade II to III developed on days +31 in patient 1 and +16 in patient 2, involving predominantly gut and liver, but sparing the skin. Thus, allogeneic PBSCT for graft failure did not cause hyperacute GVHD even with very high T cell numbers in patient 1, and graft failure with CD34 selected PBSC was successfully reversed even with a low number of T cells in patient 2.