The production of beta-glucanase in a mycoparasitic fungus, Coniothyrium minitans, was investigated using a wild type strain 2134. Through ultraviolet (UV) irradiation of strain 2134, four mutants, M11-3B2, A7-3D, A8-1 and A10-4, exhibiting enhanced P-glucanase activities were isolated. Strains A8-1 and A10-4 were constitutive mutants that expressed barley p-glucan hydrolysing activity in the absence of a supplemental inducer (beta-glucan substrate). Supernatant from A8-1 and A10-4 cultures grown in potato dextrose broth (PDB), the medium without beta-glucan, had maximum levels of beta-glucanase activity on average 10 times greater than the wild type strain 2134. M11-B32 had low levels of constitutive beta-glucanase expression and enhanced laminarin hydrolysing activity when grown in presence of beta-glucan-rich substrate. Crown Copyright