From 1976 to 1981, 25 cases of S. pyogenes septicemia were diagnosed at the University Medical Center, Lausanne, Switzerland, in 5 children and 20 adults. The twenty adult patients are described. The age range was from 24 to 94 years. The portal of entry was the skin (erysipelas, skin ulcers, surgical wounds) in 12 cases, the respiratory tract (upper 3, lower 3) in 6 cases, and the vagina in 2 cases. All except 3 patients were acutely ill with high temperature (39 degrees C) and toxic appearance. None had an underlying malignancy. The clinical course was complicated in 5 patients, i.e. septic arthritis (2), pulmonary abscess (1), endocarditis (1) and acute rheumatic fever (1). After initiation of penicillin therapy, temperature and symptoms resolved only slowly (mean 11 days). Four patients died from infection. In 2 of them the antibiotic treatment had been delayed. When a patient exhibits clinical signs of septicemia and muco-cutaneous lesions suggestive of a portal of entry, S. pyogenes septicemia should be suspected. Complications are frequent and the prognosis remains poor despite early adequate antibiotic treatment.