In the present paper the research was focused on mutual interaction between three strains of Trichoderma and nine phytopathogenic moulds. Dual biotic test was made in media imitating natural environmental conditions (milled grain of four typical cereals), which was a modification of a standard procedure. Every tested and test-strain exploited cereals as the source of nutritive compounds to a different extent, which was exhibited by various growth speed and changes in interactions. The highest antagonistic ability was demonstrated for Trichoderma harziamum T33, which in many cases caused complete growth inhibition of tested moulds. Neither of the phytopathogenic strains had a negative influence on the T33 strain, in contrast to the rest of Trichoderma strains

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