The morphology of acute rejection (AR) in biopsies of liver allografts obtained in the first 2 weeks after transplantation was analyzed. Material from patients maintained on azathioprine and prednisone (AZA; Groningen, The Netherlands) was compared with that of patients receiving cyclosporine A and prednisone (with or without azathioprine) in low doses (CSA; Minneapolis). Strict selection criteria were applied to exclude circulatory and biliary complications and viral infection in this early observation period after transplantation. Follow-up biopsies ranged from 3 weeks to 1 year after transplantation. Time zero biopsies and/or pretransplant biopsies served as baseline histology, Our data revealed an identical morphologic picture during AR early after transplantation in both patient groups, except for a more marked degree of venous endothelialitis and hepatocyte ballooning in the Minnesota material. The follow-up biopsies suggested a spontaneous resolution of these early rejection episodes without antirejection treatment in six of the ten AZA patients. No differences in the long-term survival rate between the CSA- and AZA-treated patients were observed.