Basic extracts isolated from lamb meat treated at various temperatures were tested for mutagenicity in Salmonella typhimurium strain TA98 in the presence of S9 mix. Samples of ground lamb patties were cooked for 10 min per side at 100, 150, 200, 250 and 300 degrees C. Low cooking temperatures resulted in products with low levels of mutagenicity. At temperatures greater than 150 degrees C the mutagenic activity of the cooked meat increased to reach a maximum at 300 degrees C. In another series of experiments, lamb patties were cooked at 250 degrees C for 2, 4, 6, 8, 10 and 12 min. Short cooking times (rare products) caused no mutagenic activity and uncooked ground meat showed no activity. Prolonged cooking appeared to increase the mutagenicity of the products with a maximum value at 10 min. The results indicate that the formation of mutagens depends on both cooking temperature and cooking time. The level of mutagenicity tends to increase with the degree of charring.