The lytic activity of mutanolysin from Streptomyces globisporus on 42 cultures of Actinomyces pyogenes could be effectively analyzed in an aggregometer. It was expressed as increase of transmittance at 546 nm after 20 min and 2 h at 37 degrees C. The A. pyogenes cultures revealed no uniform lysis pattern. Most of the cultures were lyzed within 20 to 40 min at 37 degrees C, others were lyzed only moderately or weakly within 2 h of incubation. The lytic activity was optimal at low (0.01 mol/l) molarity of the lysis buffer between pH 5.7 and 7 and could be inhibited by HgCl2.A. pyogenes was not lyzed by lysostaphin or lysozyme.