The residues of polycyclic aromatic hydrocarbon (PAH) and neutral organochlorine compounds in breast fat of 44 breast cancer patients and 33 women free of cancer were determined. No statistically significant differences appeared between the two comparison groups with regard to occurrence of PAH compounds. Of the neutral organochlorine compounds, residues of beta-hexachlorocyclohexane (HCH) were found more frequently in breast cancer patients. After adjusting for age and parity by stepwise logistic regression, beta-HCH remained a significant risk factor of breast cancer. Using a cutoff point for the residue level of beta-HCH in breast adipose tissue of more than 0.1 mg/kg fat, the odds ratio was 10.51 (95% CI, 2.00-55.26).