Immunoscintigraphy with technetium-99m labelled BW 250/183, a murine monoclonal antibody specific for granulocytes, yielded a false-positive result in a patient suspected of having an abscess in his renal graft. To substantiate the presumption that diathesis and unspecific accumulation of the antibody may have caused this result, ten selected patients were investigated who presented with chronic vascular graft rejection but without signs of bacterial infection. Scintiscans were recorded 4 and 24 h after administration of^99mTc-labelled BW 250/183. Graft-background ratios (GBRs) were calculated for each transplant. These were compared with the mean of physiological kidney-background ratios (KBRs) and with bone marrow-background ratios (BMBRs). After removal, the grafts were examined with pathological and immunohistological methods. Seven transplants demonstrated 4-h GBRs (mean: 3.9±1.1,P <0.001) significantly="" outside="" the="" range="" of="" normal="" kbrs="" while="" three="" were="" within="" the="" normal="" range="" (mean:="" 1.8±0.4).="" the="" relation="" between="" 4-h="" and="" 24-h="" gbrs="" varied.="" after="" 24="" h="" five="" gbrs="" still="" remained="" increased="" (mean:="">P <0.05). by="" contrast="" the="" bmbrs="" decreased="" uniformly="" by="" 18%±5%.="" after="" graft="" removal,="" histopathology="" demonstrated="" no="" dominant="" granulocyte="" accumulations="" but="" various="" degrees="" of="" chronic="" vascular="" and="" tubulo-interstitial="" rejection.="" immunohistochemical="" studies="" did="" not="" indicate="" cross-reactivity="" of="" bw="" 250/183.="" increased="" gbrs="" of="" longstanding="" renal="" allografts="" indicate="" the="" passage="" of="" the="" antibody="" through="" injured="" vascular="" walls="" rather="" than="" the="" presence="" of="" granulocyte="" accumulations.="" therefore,="" variability="" of="" gbrs="" with="" time="" reflects="" changes="" in="" transitory="" concentrations="">^99mTc-labelled BW 250/183 in the tissues.