The association of the arylamine N-acetyltransferase polymorphism and breast cancer has been investigated by analysis of genomic DNA from 160 breast cancer patients and 132 healthy women. Five mutations of the NAT2 gene were studied by using allele-specific PCR amplification and restriction mapping with the endonucleases FokI and Ddel. Eight allelic variants of the NAT2 gene were identified in both, patients with breast cancer and control groups, with relative frequencies. Wild-type 0.194 and 0.219, 341C+481T+803G 0.433 and 0.345, 341C+481T 0.048 and 0.076, 282T+590A 0.205 and 0.222, 282T 0.059 and 0.044, 590A 0.011 and 0.024, 803G 0.016 and 0.052, 857A 0.035 and 0.019, respectively. The prevalences for the poor acetylator genotypes were 53 and 51% for the patients with breast cancer and the control group, respectively. Seven patients with the rare lobular breast cancer showed reduced frequency for NAT2 mutations (p < 0.05) and all of them had the extensive acetylator genotype (p < 0.01). This preliminary observation suggests that extensive acetylation may be related to lobular breast cancer. No genetic support for association of the NAT2 polymorphism and other histologic types of breast cancer was found. Any differences in the acetylator rate between breast cancer patients and healthy subjects may be secondary to breast cancer itself, but not involved in the pathogenesis of the disease.