Wethers equipped with a rumen fistulae were subjected to four dietary treatments in consecutive experiments. The treatments consisted of rations containing wheat grain and pasture hay at a ratio of 1 to 1 on a dry matter basis. Two wheat grain batches were fed either in the absence or presence of a detoxifying agent (Mycofix^®Plus, Biomin GmbH, Herzogenburg, Austria). One wheat grain batch served as the uncontaminated control wheat whereas the other batch contained the Fusarium toxins deoxynivalenol (DON) and zearalenone (ZON) at concentrations of approximately 10 and 0.76 mg per kg dry matter, respectively. Parameters of rumen fermentation such as the molar ratios of short chained volatile fatty acids and ammonia concentration in rumen fluid remained unchanged in response to dietary treatments whereas the detoxifying agent exerted a rumen pH-buffering effect. This effect was independent of the mycotoxin contamination of the wheat. The pH-differences in rumen fluids collected from wethers fed the MP-supplemented and unsupplemented rations amounted 0.2 to 0.3 on average in the time period between 1.5 and 5 h after feeding. The kinetic profile of the in sacco dry matter degradation revealed a reduced degradation rate for wheat straw incubated in wethers fed the mycotoxin contaminated rations whereas no changes were obvious when lucerne hay was incubated. The detoxifying agent had no effect on the kinetics of dry matter degradation. It can be concluded that feeding of rations containing approximately 4.6 mg of DON and 0.34 mg ZON per kg of complete ration at a reference dry matter content of 88% does not impair rumen fermentation although there was a trend for a decrease in the rate of dry matter degradation of the slowly degradable wheat straw. The pH-buffering effects of the detoxifying agent were mycotoxin independent.