In a prospective randomized study, 25 recipients of primary cadaveric renal grafts with immediate onset of function were studied. Thirteen patients were submitted to a "base line" angiography of the graft on days 5 to 11 after transplantation, while 12 patients served as controls. HLA compatibility, pretransplant blood transfusions, and recipient age differed only slightly between the two groups. Six of 13 patients in the angiographed group showed clinical evidence of acute rejection within the first 14 days after grafting; of these rejections, two were diagnosed prior to angiography. In the control group, 9 of 12 patients rejected their grafts within the first 2 weeks. Thus, there was no indication that renal angiography in the early post-transplant period precipitated acute rejection crises, as has earlier been suggested.