this study aimed to investigate in a population of brazilian patients with multiple sclerosis (ms) single-nucleotide polymorphisms (snp) in the promoter region of il4 (*33c-t) and receptor il4r (*q551r a-g) genes proposed to interfere with disease progression. no significant differences were observed in either of the snps investigated between healthy controls (n=135) and ms patients (n=129). however, the il4+33 tt genotype was significantly (p=0.039) higher in african descendants ms (af-ms= 9.09%) than in caucasian ms (ca-ms= 1.35%). it was also observed a significant (p=0.016) increase for the il4r* q551r cc genotype in af-ms compared to those of caucasian ethnicity (af-ms= 21.62%; ca-ms= 4.35%). these results suggest that il4+33 and il4r*q551 polymorphisms may have a disease-promoting role of th2 mediators in african ms descendants. additionally neither il4 nor il4r genes are susceptibility factors for brazilian ms but may be able to modify ethnicity-dependent disease risk and penetrance of susceptibility factors.