The concentrations of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and DiMeIQx (i.e. the sum of 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline and 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline) were determined as their 3,5-bis(trifluoromethyl)benzyl bromide derivatives in commercial heat-processed daily Finnish foods using the gas chromatography-mass spectrometry technique with negative chemical ionization. With this technique it was possible to detect picogram quantities of halogenated aminoimidazoazaarene (AIA) derivatives. The mutagenic activities of the food samples were tested using the Ames Salmonella assay. The mutagenicities and amounts of the AIA compounds analysed varied considerably in the food samples. All the flame-broiled fish samples and the majority of the grilled pork and chicken samples were positive in the test; of all the food samples tested fish samples had the highest mutagenic activity. Industrially produced meat patties were non-mutagenic. The amounts of MeIQx, DiMeIQx and PhIP in grilled products that exhibited mutagenic activity varied in the range 0.04 to 0.4, 0.03 to 0.2 and 0.5 to 3.8 ng per g cooked food, respectively. Some of the highly mutagenic flame-broiled fish samples contained only PhIP, the amount of which varied from 0.5 to 5.5 ng per g fish. One of the samples also contained a small amount of MeIQx. None of the non-mutagenic meat patties contained detectable amounts of MeIQx, DiMeIQx or PhIP. In this screening study evaluation of the occurrence of AIA compounds was carried out in a relatively wide range of commercial heat-processed Finnish foods. Considerable differences between equivalent products from different manufacturers were found in many cases. This variation indicates that industrial processing of food has a marked effect on the mutagenic activity of the product.