The relationships between DNA adducts and birth weight and between birth weight and genetic polymorphisms of metabolic genotypes were studied using DNA from the children part of placental samples. The samples were collected in the districts of Teplice and Prachatice and in the city of Prague. DNA adducts were analyzed by (32)P-postlabeling in a total of 199 subjects, genetic polymorphisms in 1013 subjects. GSTM1, GSTP1, GSTT1, CYP1A1*2A, and CYP1A1*2C genotypes were determined for each subject. The level of DNA adducts was not correlated with birth weight in any group (N=199), including that from the polluted district of Teplice (N=90). Birth weight was significantly decreased by smoking, ETS and alleles of CYP1A1*2C. The risk of low birth weight and prematurity was significantly increased by genotypes of GSTM1 and CYP1A1*2C and the combination GSTM1+CYP1A1*2A. Genotypes are primarily effect modifiers, whose effect incorporates the effect of environmental factors. This means that in the future, the impact of air pollution on children's health should be studied together with their genetic polymorphisms.