In order to prevent the adverse effects of a first OKT3 injection in renal transplant recipients, we administered polyclonal antilymphocyte globulins (ATG Fresenius, 4 mg/kg/j) for 3 days before OKT3 injection. Compared with a historical group of 5 patients who did not receive ATG pretreatment before OKT3 injection, the patients who were pretreated by ATG had a significantly lower absolute number of circulating lymphocytes before the first OKT3 injection (363 +/- 107 vs 1,230 +/- 80/mm3, P < 0.001), a lower raise in plasma TNF-alpha level 2 hours after OKT3 injection (178 +/- 42 vs 735 +/- 127 pg/ml, P < 0.005) and a significant decrease in frequency and intensity of clinical symptoms, mainly chills, dyspnea, and headaches. However, fever and peak creatinine level were similar in both groups. A 80 percent success rate of crisis treatment was achieved in both groups and there was no increase in infectious complications. In conclusion, pretreatment with ATG induces a lymphocyte depletion, and decreases the amounts of TNF-alpha released as well as the side-effects of a first OKT3 injection.