Streptococci are amont the most common bacterial pathogens physicians encounter in practice. Infections with streptococci continue to occur with significant frequency despite the general sensitivity of these organisms to a variety of widely used antibiotics. In newborn infants and other special patient groups, streptococci may produce fulminant and fatal sepsis (Table 1). In normal children and adults, infections usually are short term and often mild or unrecognized but with the possibility of resulting, unpredictably, in nonsuppurative complications some weeks or months later. Although scarlet fever has become an unusual and clinically attenuated disease, its rashless analog, streptococcal pharyngitis, presents thorny problems in the differential diagnosis of symptomatic patients and in the detection of subclinical infections. Erysipelas now is a rare disease, but recent studies have confirmed that streptococci often are the primary etiologic agent in impetigo, another type of skin infection--with peculiar bacteriologic and epidemiologic features. Infections with group D streptococci have always been a special case because of their frequent resistance to penicillin, and group B streptococci (also somewhat resistant) present special problems in the perinatal period. Streptococci may appear in unexpected places or guises (see Table 1). Thus, the modern physician has little reason to relax in his vigilance for and knowledge of streptococcal infections.