Thirteen commercial meat-flavour samples were analysed for creatine and creatinine content and tested for mutagenicity in the Ames Salmonella/microsome test. In most samples, more than 50% of the creatine had been converted to creatinine. Mutagenicity was related to the creatinine content: 150 mumol creatinine/g dry matter (gdm) gave upwards of 2500 revertants/gdm, concentrations of 15-40 mumol/gdm gave about 100 revertants/gdm and concentrations of 1-10 mumol/gdm gave only low or no significant mutagenicity. No relationship was apparent between coloration and mutagenicity. Beef steaks (initial weight c. 500 g) baked at oven temperatures between 115 and 245 degrees C only showed significant mutagenicity--135 revertants/100 gE (initial raw weight)--in the crust when baked at the highest temperature (245 degrees C). The gravies (meat-juice drip) collected during baking showed a linear increase in mutagenicity with baking temperatures up to 180 degrees C (48-828 revertants/100 gE) and a very sharp increase in mutagenicity for the gravy collected from beef steak baked at 245 degrees C (28,300 revertants/gdm or 19,800 revertants/100 gE). At this high temperature, the brown coloration and the proportion of creatinine to total creatine and creatinine were also dramatically increased, because this gravy dried up completely during the baking procedure.