Cereal grains are part of the most important alimentary sources for humans and must be safely stored, as contamination by living organisms, such as insects and fungi, causes quantitative and qualitative losses. Tribolium castaneum is one of the most common insect pests of stored products, and may also produce benzoquinones as a defensive action. This insect presence makes the products more susceptible to the spread of fungi, such as Aspergillus flavus, which alters the quality of the grains and may produce mycotoxins, such as aflatoxins. The aim of this work was to evaluate the influence of adults of T. castaneum presence on a mycotoxigenic strain of this fungi development and production of mycotoxins, as well as the influence of the fungi on insect adults. Maize flour was exposed to: T. castaneum adults; spores of A. flavus; both organisms; and only maize as control. In all assays, except control, AFB₁ and total aflatoxins content were above the accepted limit for human food. The ability of these organisms, to thrive under the same conditions and the chemical compounds released by them, makes the interaction between T. castaneum and A. flavus a subject with great importance to the stored maize safety.