The β-1,3-glucanase system of the mycoparasitic T. harzianum, isolate T-Y, was found to be composed of at least five different enzymes. Their migration distance in acrylamide gels corresponded to peptides with molecular masses of 30–200 kDa, and they were named accordingly. The largest enzyme – Gβ-1,3–200, was the most abundant when T-Y was grown with no carbon source. Its secretion was almost eliminated when T-Y was grown on media containing a high concentration of carbon sources such as N- acetylglucosamine (GlcNAc) or malic acid. Several isolates of T. harzianum were found to have a β-1,3-glucanase secretion system, controlled by catabolite repression. Each isolate exhibited a different β-1,3-glucanase profile. Gβ-1,3–200 was isolated and purified: its molecular mass was approximately 75 kDa, and its activity was of the exo-type, specific to β-1,3-glucan linkages. Four short peptides resulting from proteolysis of this enzyme were sequenced, and their sequences were most homologous to LAM1.3, a previously isolated β-1,3-glucanase.