Mycotoxicoses have been recognized worldwide to cause problems in animal production. Trichothecene mycotoxins, for the most part produced by Fusarium spp., have obtained particular importance. Between 1982 and 1984, 295 samples of feedstuffs (cereals and mixed feeds) have been analyzed on natural occurrence of type-A trichothecenes. The skin toxicity test with guinea pigs was used as a screening method. Analysis of trichothecenes by capillary gaschromatography with flame ionization detection was complicated by interfering substances from the complex matrix of the sample-material. Definite results were only obtained by the use of gaschromatography-mass spectrometry. In comparison to the electron impact ionization the chemical ionization technique showed to be advantageous. Forty-two of the 295 samples analyzed were found to be positive in the biological assay. Nine of these positive samples contained trichothecenes as determined by mass spectrometry: T-2 toxin in mixed feed (65 micrograms/kg); oats (80 and 86 micrograms/kg) and wheat (100 micrograms/kg); diacetoxyscirpenol in mixed feed (125 micrograms/kg) and wheat (50 micrograms/kg); neosolaniol in oats (310 and 350 micrograms/kg); HT-2 toxin in oats (700 micrograms/kg). Oats proved to be contaminated more frequently as compared to the other cereals and the analyzed mixed feeds.