To study the effects of level of intake on ruminal fermentation, 14 dairy cows equipped with ruminal and duodenal cannulas were fed different amounts of the same diet. The diet consisted of 60% concentrate including 55% wheat (Fusarium-contaminated and control) and 40% maize- and grass silage (on DM-basis). Each cow was fed contaminated and control wheat. Rumen fermentation was not significantly influenced by the contamination, however the increased feed intake decreased pH, fermentation of organic matter (FOM), of protein and of neutral detergent fibre. Efficiency of microbial protein synthesis (g MP/kg FOM) was not linearly related to level of intake.