When a marine-isolate, Chaetomium globosum was cultivated in a medium with an increased MgCl2 content, a bacteriolytic enzyme was extracellularly produced. The enzyme was purified approximately 130-fold. It lyzed Staphylococcus aureus, Micrococcus lysodeikticus and several other Gram-positive bacteria. Optimal pH and temperature for the lysis were 8.0 and 37°C, respectively. The enzyme was heat-labile with maximum stability at neutral pH. Enzymatic activity was greatly stimulated by NaCl and CaCl2 with maximum activity obtained in the presence of 0.1 M NaCl and 0.003 M to 0.005 M CaCl2. The activity was stimulated by SH-compounds and was inhibited by SH-reactants.