To investigate the correlation between the single nucleotide polymorphisms (SNP) of +33C/T in the promoter region of IL-4 gene and +1923C/T in intron-3 region of IL-13 gene and the susceptibility of asthma, and to study the impact of these polymorphisms upon total serum IgE levels.The 2 polymorphisms were determined by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP), in 150 asthmatic subjects (asthma group) and 160 healthy controls (healthy control group) of the Han nationality in Shandong province enrolled from December 2003 to June 2007. The total serum IgE levels were determined by ELISA.The genotype frequencies of CC, CT and TT in +33C/T sites of IL-4 gene were 43% (68/160), 35% (56/160), 22% (36/160) respectively in the controls, and 18% (27/150), 36% (54/150), 46% (69/150) respectively in the asthmatic subjects. The genotype frequencies of CC, CT and TT in +1923C/T sites of IL-13 gene were 41% (66/160), 43% (68/160), 16% (26/160) respectively in the controls, and 21% (31/150), 38% (57/150), 41% (61/150) respectively in the asthmatic subjects. The distribution of genotype in each sites between the 2 groups was significantly different (chi(2) = 27.821, 26.544 respectively, all P < 0.01). The CT and TT genotypes carried higher risks for asthma than CC genotypes (chi(2) = 21.870, 14.206 respectively, all P < 0.01). The total serum IgE levels of CC, CT and TT in +33C/T sites of IL-4 gene were (92 +/- 37), (122 +/- 45), (146 +/- 44) KU/L respectively in the controls, and (179 +/- 40), (294 +/- 51), (341 +/- 80) KU/L respectively in the asthmatic subjects. The total serum IgE levels of CC, CT and TT in +1923C/T sites of IL-13 gene were (85 +/- 31), (102 +/- 38), (144 +/- 49) KU/L respectively in the controls, and (186 +/- 65), (297 +/- 87), (363 +/- 140) KU/L respectively in the asthmatic subjects. In these 2 sites, the total serum IgE level of asthmatics was higher than that of the controls with the same genotype between the 2 groups (t = 4.653, 6.547, 7.754; and 4.673, 6.784, 8.157 respectively, all P < 0.01). The total serum IgE levels of CT, TT genotypes were higher than CC genotypes in the same group (t = 5.748, 6.253 respectively, all P < 0.01).There was a significant correlation between the polymorphisms of +33C/T sites of IL-4 and +1923C/T sites of IL-13 gene and susceptibility to asthma and increase of the total serum IgE. The IL-4 gene and IL-13 gene may be important candidate genes for asthma.