Different actinomyces species (25 strains) were studied and Actinomyces cellulosae 41 was found to be the most active one in its capacity to cause lysis of Saccharomyces cerevisiae intact cells as well as in the production of 1,3-beta-glucanase. The enzyme preparation containing 1,3-beta-glucanase can be obtained from the filtrate of the actinomycete cultural broth after 60 h of growth by precipitation with four volumes of ethanol. The optimal pH for the action of 1,3-beta-glucanase from A. cellulosae is 5.5. Hydrolysis of laminarin (5 mg of the substrate) yields 2.4 mg of reducing sugars or 13.3 microM (recalculated per glucose). There is a direct correlation between the amount of produced reducing sugars and the enzyme concentration up to 10 microM/ml (recalculated per glucose). The enzyme hydrolysate contains glucose and oligosaccharides with a different degree of polymerization. Therefore, the enzyme is endo-1,3-beta-glucanase. It produces less quantities of the disaccharide than those of glucose and trisaccharide. The enzyme yields only traces of glucose upon prolonged hydrolysis of p-nitrophenyl-beta-D-glucoside (PNPG) and shows a weak capacity for transglycosylation when laminarin is used as a donor and PNPG as an acceptor.