OBJECTIVE: P-glycoprotein 170 (P-gp) is a plausible biologic candidate for pharmacoresistance in epilepsy. The expression and efflux efficiency of P-gp is influenced by a polymorphism (C3435T) in the encoding gene (MDR1). The CC genotype at the MDR1 C3435T polymorphism was reported to be associated with the response to antiepileptic drug treatment. This study attempted to replicate this finding by examining the association of this genetic polymorphism with response to antiepileptic drug treatment in ethnic Han Chinese children with epilepsy. METHODS: Two hundred and fourteen ethnic Han Chinese children with epilepsy were classified based on the response to antiepileptic drug treatment: drug-nonresponsive and drug-responsive. DNA samples were obtained from the patients. Genotypes of the C3435T polymorphism were determined by traditional polymerase chain reaction followed by restriction digestion (PCR-RFLP). The frequency of genotypes and alleles between the two groups was compared by Chi-square test. RESULTS: Of the 214 patients, 164 were dru-responsive and 50 were drug-nonresponsive. There were no significant differences in the allele frequency and genotype frequency between the two groups. CONCLUSIONS: There is no an association between the CC genotype or C allele at the locus of C3435T in MDR1 gene and response to antiepileptic drug treatment in ethnic Han Chinese children with epilepsy.［Chin J Contemp Pediatr, 2007, 9 (1):11-14］