The mutagenicity of pan-fried patties of five bovine tissues (meat, heart, tongue, liver and kidney) containing various concentrations of creatine, monosaccharides and free amino acids were studied. Two experiments were performed, one on single tissues fried at 150, 175 or 200 degrees C for 3 min and the other on mixtures of meat and one of the other four tissues in various proportions, fried at 200 degrees C for 3 min. For both experiments, a double-sided Teflon-coated plate was used. Frying at 150 degrees C induced mutagenicity to Salmonella typhimurium strain TA98 only in the heart sample-6000 revertants/100 gE (grams initial raw weight). Meat, heart and tongue fried at 175 or 200 degrees C showed mutagenicity values between 6000 and 19,600 revertants/100 gE. A linear relationship between mutagenicity and temperature was obtained for each of the three muscles and creatine was converted to creatinine with increasing temperature. Liver or kidney samples fried alone showed insignificant mutagenicity at all three temperatures. The creatine plus creatinine levels of raw meat, heart and tongue samples were between 19 and 33 mumol/g wet tissue. Liver and kidney both showed very low amounts of creatine plus creatinine (about 2 mumol/g wet tissue) in the raw tissue, while free amino acids were high. Glucose levels were high in liver but low in kidney samples. In meat/heart and meat/tongue mixtures the mutagenicity varied between 10,800 and 17,300 revertants/100 gE. The meat/liver and meat/kidney mixtures showed linear relationships between mutagenicity and the proportions of the mixture. The values for the slopes and intercepts of the two lines were almost equal. Among the three groups of precursors (creatine plus creatinine, monosaccharides and free amino acids) the creatine plus creatine in raw tissue seems to be the most important for producing mutagenicity. However, in crusts, the creatinine concentration was the variable with which most of the mutagenicity was associated.