A beta-1,3-glucanase from the culture supernatant of Oerskovia xanthineolytica TK-1 grown on minimal medium containing yeast glucan as the carbon source was purified to an electrophoretically homogeneous state by means of chromatography using DEAE-Sephacel, DEAE-Toyopearl 650 M and Bio-Gel P-2 column. The molecular mass was 40,000 Da and the pi was 6.5. The optimum pH was 7.5 and 5.5 when assayed on laminarin and yeast glucan, respectively. The enzyme had an affinity for yeast glucan and could lyse living yeast cells without the need for a second lytic component, an alkaline protease. Hydrolysis of yeast glucan was endolytic, yielding a mixture of glucose and biose. The N-terminal amino acid sequence of the enzyme showed no homology with that of a related beta-1,3-glucanase from the same genus.