SUMMARYAn outbreak of streptococcal pyoderma in a military institution into which fresh susceptible recruits were regularly introduced involved more than 1300 persons over an eighteen-month period. Two M types were responsible for the great majority of the cases and an attack by one conferred immunity to that strain but not to the other. Lesions varied from trivial to disabling. Epidemiological studies indicated that contact -direct or indirect -through such things as gymnasium equipment and room dust was the means of transmission. The outbreak was eventually controlled by vigorous case finding, thorough treatment of cases and the strict application of hygienic principles to prevent spread. There were no late complications and throat streptococci were not involved. It is possible to control such an outbreak without isolation or the making of any significant concessions in the training programme even when large numbers of persons are living and working at close quarters.