Rheumatic fever has been considered a major problem among civilians in the United States and elsewhere for 100 years but was not recognized as a concern among the U.S. military until World War II. At that time the only available control measure was antimicrobial prophylaxis of recurrent rheumatic fever. Subsequent studies, conducted primarily by the Streptococcal Diseases Laboratory of the Armed Forces Epidemiological Board, demonstrated that rheumatic fever could be prevented by the treatment of patients with streptococcal pharyngitis and by the administration of penicillin for the prophylaxis of streptococcal infections in large groups. With the use of available preventive measures, rheumatic fever virtually disappeared by the 1970s. In 1985, however, rheumatic fever and severe streptococcal infections reappeared, first in the Rocky Mountain area. It is speculated that this reappearance was due to special strains of group A streptococci and--in severe cases--the production of pyrogenic exotoxins. At present, cases continue to occur but not at the level seen in the late 1980s.