Because of the allelic variations within the M protein gene (emm gene) of group A streptococci, reliable typing of this important human pathogen can be accomplished by the use of emm gene-specific oligonucleotide probes. Two technical modifications (a reverse dot blot and a reverse line blot hybridization assay) of a novel approach for the type-specific identification of emm genes have been developed. Both procedures involved amplification of an emm gene by polymerase chain reaction. The non-radioactively labeled amplicon was subsequently hybridized to a membrane carrying an array of immobilized emm gene-specific oligonucleotide probes, thus allowing the simultaneous analysis of the gene polymorphism in a single hybridization reaction. The feasibility of these rapid and easy to perform methods was shown for the unequivocal identification of reference strains and clinical isolates belonging to 16 different M serotypes.