We studied about the histological findings of the kidneys including of the infiltrated macrophages in one hour post-transplantation kidney biopsies (one hour biopsies) and re-biopsies on 11 patients. They were transplanted at 4-28 (ave. 15.1 +/- 3.8) years of age. The periods from transplantation to this study were 1.0-7.3 (ave. 3.3 +/- 1.9) years. 6 patients had acute rejections, and their renal function became normal after treatments. At this study, all grafts survived, and the patients had no abnormal findings except two (one had proteinuria, another had proteinuria and mild elevation of serum creatinine level). But histologically, five patients had chronic rejections among the 8 patients who had re-biopsies more than one year after transplantation. And we experienced 6 patients whose kidney had mesangial IgA deposits in one hour biopsies and 3 patients who had de novo type glomerulonephritis in re-biopsies (IgA neuropathy in 2 patients, membranous nephropathy in one). In one hour biopsies, the populations of macrophages in the interstitium were 4.18 +/- 2.84/mm2 in the patients who would have acute rejections (6 patients), 1.38 +/- 1.13/mm2 in the cases who would not have. It was suspected that the increase of the infiltrated macrophages in the interstitium in one hour biopsies could predict acute rejections. In re-biopsies, many macrophages infiltrated in the interstitium (8.34 +/- 4.86/mm2), particularly on patients who had chronic rejections.