The content of fungal biomass essentially impacts the quality assessment of food products. In this paper, the content of ergosterol (ERG) was presented, i.e. of a fungal biomass bio-indicator in cereal grain, in breakfast foodstuffs containing bran and flakes that were purchased in shops of a retail network in Poznań in 2008, as well as in flours and in the products milled in a laboratory. The highest mean content of ERG was found in oat bran: 30.71 mg/kg, whilst the lowest ERG content, among all the bran types analysed, was reported in wheat bran: 9.98 mg/kg. Among all the corn flakes tested, the oat flakes were reported to contain the highest amount of ERG: 8.04 mg/kg, and the wheat flakes – the lowest: 0.97 mg/kg. The products containing additives in form of dehydrated fruits had a higher amount of ERG than the analogous products without additives. The rye, barley, oat, and wheat flours were also investigated. The content of ERG in the flours and in the bran tested was compared; it was found that the content of this metabolite was comparable in all the cereal types, and, as for the flours, it was lower by about 97 %. The content of this metabolite in the bran tested was higher if compared with the non-processed grain, and the ERG concentration was higher by about 50 %. In addition to the above mentioned milled products, the content of ERG was also analyzed in the grain gathered in 2008 and stored in cereal storage silos. Here, the highest ERG concentration was found in the oat grain: 16.11 mg/kg, and the lowest in the wheat grain: 4.13 mg/kg.