In our effort to find an optimum immunosuppressive protocol for kidney transplantation we introduced two forms of ATG prophylaxis: 1. high-dose single-bolus prophylaxis (9 mg/kg) in non-sensitized patients (PRA < 5%); and 2. low-dose 8-day prophylaxis (1.5-3.0 mg/kg) in sensitized patients (PRA > 5%). A total of 204 kidney graft recipients were included in this study and treated with a triple-drug therapy (TDT). In comparison with TDT-treated controls, in sensitized patients the 8-day ATG prophylaxis resulted in a reduced rate of rejection episodes (25.5% vs 47%), an improved 1-year graft survival (82% vs 71%) and patient survival (94% vs 90%). In non-sensitized patients the high-dose single-bolus ATG prophylaxis induced a T-cell lymphopenia lasting 4 to 5 days and, in comparison with the corresponding controls, resulted in a shortened hospital stay (31.2 days vs 36.7 days), a reduced rate of rejection episodes (25.5% vs 53%), an improved 1-year graft survival (92% vs 86%) and patient survival (100% vs 94%).