Thirty patients under the age of fifty underwent technically successful simultaneous pancreas/kidney transplantation (SPK). Twelve patients received donor bone marrow (DBM) as either one (5 patients) or two (7 patients) doses during week one and/or week two. Fresh marrow was used on day 0 in three patients, otherwise the bone marrow was cryopreserved. The total dose of DBM (vertebral bodies) infused into each recipient was =< 5 x 10 8 cells/kg. Eighteen patients did not receive DBM (controls). Immunosuppression consisted of OKT3 induction therapy, azathioprine, FK506, and steroids for all recipients. In the DBM group there were five episodes of biopsy proven acute rejection (AR) (40%). In the control group there were six episodes of biopsy proven AR and six other patients who were treated empirically for a rise in creatinine (total 67% AR). No grafts in either group were lost to rejection. The degree of chimerism was assessed in peripheral blood (PB) using flow cytometry to detect donor allo-specific class II protein epitopes. The table below demonstrates a greater degree of chimerism in the DBM group in the PB over time (P = .0283 students t test unpaired variables):Peripheral blood (PB) chimerism persists as late as one year following SPK in the DBM group.