A murine IgG1 monoclonal antibody, 25–3 (Immunotech, France), directed against the α chain (CD11a) of the human LFA1 molecule was used in the treatment of 7 histologically documented first acute rejection in first kidney transplantations under cyclosporine. Four patients (group I) received 20 mg/day for 2 days and 10 mg/day for 8 days of 25–3 MoAb. One developed Quincke's edema after the first injection of 25–3 and was immediately withdrawn from the study. In 2 patients, whose serum creatinine continued to increase, 25–3 MoAb was replaced by steroids, followed by ALG after 3 and 4 days of treatment, respectively. In the last case, rejection was reversed by 25–3 MoAb alone. As the clinical response of rejection to 25–3 was poor, another group of 3 patients (group II) was treated with 25–3 at a dose of 40 mg/day for 2 days, 20 mg/day for 2 days, and 10 mg/day for 6 days, but 25–3 was still unsuccessful in reversing acute rejection, and rescue treatment was initiated between days 5 and 8 in all cases. MoAb tolerance was excellent in 3 patients. With the exception of the one case of Quincke's edema, only minor side effects were noted in the last 3 recipients.