A scheme for "fingerprinting" of Actinomyces pyogenes strains based on their production of (P-typing) and the sensitivity to (S-typing) bacteriocin-like substances has been developed. P-typing and S-typing of 42 A. pyogenes cultures with a set of 9 micrococcal and staphylococcal species as indicator strains and 9 streptococcal species as bacteriocin producer strains revealed 10 P types and 7 S types, respectively. The bacteriocin "fingerprinting" procedure might provide a means for subdividing A. pyogenes and may find application in epidemiological studies.