BACKGROUND: Steroid pulse therapy has been used for patients with acute rejection after kidney transplantation. The ABCB1 gene codes for P-glycoprotein, a transporter that is involved in the metabolism of steroids. However, the role of ABCB1 polymorphisms has not been investigated in patients with acute rejection after kidney transplantation. METHODS: Among 763 patients that received kidney or simultaneous pancreas-kidney transplantation at Seoul National University Hospital between May 1996 and July 2009, 684 patients agreed to genetic sampling for polymorphisms. Acute rejection was defined as biopsy-proven, acute cellular rejection with increased serum creatinine, or in the context of delayed or slow graft function. Steroid-resistance was defined as no improvement in serum creatinine, need for additional OKT3 or ATG treatment, or repeated acute rejection within 30 days. Three polymorphisms of ABCB1 gene (C1236T, C3435T, G2677T/A) were assessed. RESULTS: C allele frequency of C3435T was 59.3% and of C1236T 40.1%. Patients who were steroid-resistant (n=37) had higher serum creatinine at kidney biopsy compared to those who were steroid-sensitive (n=49, P<0.001). The frequency of ABCB1 gene polymorphisms (C1236T and C3435T) did not differ significantly between patients who were steroid-sensitive and those who were resistant. An association with G2677T/A could not be analyzed due to a high failure rate of genotyping. CONCLUSIONS: ABCB1 gene polymorphisms (C1236T and C3435T) were not associated with steroid resistance in patients with acute cellular rejection after kidney transplantation.