Heterocyclic amines (HAs) are carcinogens produced by high-temperature cooking of meat and animal protein; metabolism of HA is influenced by polymorphisms in the N-acetyltransferase-2 (NAT-2) gene. Data from a variety of sources suggest that HA may play a role in human carcinogenesis. We examined the associations between meat intake and cooking method, acetylator genotype and breast cancer risk in a sub-cohort of 32,826 women in the Nurses' Health Study who gave a blood sample in 1989-1990. Women who were diagnosed with breast cancer (n = 466) after blood draw and prior to June 1, 1994, were matched to 466 controls. Overall, rapid acetylators were not at increased risk of breast cancer compared with slow acetylators (multivariate OR = 1.1, 95% CI 0.8-1.5), and there were no associations between meat intake or cooking method of meat and breast cancer risk. Rapid acetylators with the highest red meat intake (one or more servings per day) were not at increased risk of breast cancer compared with slow acetylators with the lowest red meat intake (OR = 1.1, 95% CI 0.7-1.8). Frequent intake of charred meat among rapid acetylators (one or more times per week) was not associated with increased risk (OR = 1.2, 95% CI 0.6-2.3) compared with slow acetylators who ate charred meat less than once per month. We observed no significant associations for rapid acetylators who frequently consumed beef, pork or lamb cooked with high-temperature cooking methods, such as barbecuing (OR = 0.9, 95% CI 0.4-1.9) or roasting (OR = 0.9, 95% CI 0.5-1.6). Our data suggest that HAs may not be a major cause of breast cancer, although we cannot exclude misclassification of HA intake as the reason for the lack of association. We observed no evidence of differential susceptibility to these exposures by NAT2 genotype.