AbstractThe carcinogenic effect of flour infested with beetles (Tribolium castaneum),biscuits made of this flour, and 1,4‐benzoquinone (a quinoid secretion of this beetle) was investigated using Swiss albino mice. Force feeding flour infested withT. castaneuminduced liver and spleen tumors (lympholeukemia) in 35.2% of the animals. The tumor incidence was 29% in mice force fed biscuits made of infested flour, and the tumors were located in the liver (lympholeukemia) and breast (adenocarcinoma type A). In animals fed 1,4‐benzoquinone, the tumor incidence was 33.6%, and the tumors were located in the liver and spleen (lympholeukemia). It is speculated that 1,4‐benzoquinone, alone or in combination with other quinoid secretions of the beetles present in the flour, may be responsible for tumor induction in the organs of mice.