We describe a female patient who, despite negative conventional cross-matches, lost her first kidney graft in an acute humoral rejection. Prior to the second, AB0-incompatible (A1B to A1) living-donor kidney transplant, the patient had negative T- and B-cell cross-matches but had a positive donor-reactive endothelial cell cross-match. Following pre-transplant protein A and GlycoSorb-ABO immunoadsorptions to remove blood group B and anti-endothelial cell antibodies, Mabthera, and IVIG administrations, she was successfully transplanted. By the second post-operative day, creatinine levels were down to 96 micromol/L from 611 micromol/L pre-operatively. On day 9 creatinine rose again, and on the same day the endothelial cell crossmatch became positive for IgG, whereas the T-cell cross-match remained negative and the anti-A1B titers remained low. A kidney biopsy taken on day 10 post-transplant showed a picture of an acute vascular, antibody-mediated rejection. Following rejection treatment and repeated protein A and Glyco-Sorb-ABO immunoadsorptions, the patient's kidney function was again normalized. The use of a recently developed kit (XM-ONE) for the detection of anti-endothelial cell antibodies allowed us to identify a patient at risk for developing acute antibody-mediated rejection as well as to monitor treatment efficacy and post-transplant complications.