Trichoderma species are readily isolated from Brazilian cerrado soil by conventional methods and some of them were characterized as Trichoderma koningii. The effect of carbon source on the production of beta-1,3-glucanases in the culture filtrates of a specific Trichoderma koningii strain (ALL 13) was investigated. Enzyme activity was detected in all carbon sources tested and only one band of beta-1,3-glucanase was detected in non-denaturing PAGE. This enzyme was purified by Sephacryl S-200 gel filtration and Phenyl Sepharose CL 4B chromatography. A typical procedure provided 105-fold purification with 13.4% yield. The molecular weight of the purified enzyme was 75 kDa as estimated by SDS-PAGE. The enzyme hydrolyzed laminarin in an endo-like fashion to form small oligosaccharides and glucose. The K-m and V-max values for beta-1,3-glucanase, using laminarin as substrate, were 0.148 mg.mL(-1) and 0.159 U.min(-1), respectively. The pH optimum for the enzyme was pH 4.6 and maximum activity was obtained at 50 degrees C. Hg2+ inhibited the purified enzyme.