In recent years, several DNA fingerprinting methods have been tried for the epidemiological investigation of Streptococcus pyogenes isolates. We chose the Random Amplified Polymorphic DNA (RAPD) method for the typing of pre- and post-antibiotic treatment S. pyogenes isolates obtained from 14 patients with pharyngotonsillitis. Isolates from 4 patients had been collected 10 years earlier than from the others. Hence epidemiological connections between the strains were unlikely. Both pre- and post-antibiotic treatment isolates showed identical RAPD patterns, indicating that recurrences in these patients had been caused by homologous strains of S. pyogenes. It was possible by means of RAPD to differentiate between 12 different T-types and occasionally between clones of the same serotype of S. pyogenes. The RAPD method is an easier alternative to traditional DNA-typing techniques and provides quick results with minimal technical complexity.