The clinical course of necrotizing fasciitis in 8 patients is compared with observations on 22 other patients with erysipelas. In necrotizing fasciitis the early erythematous areas turn into a dusky blue colour with later vesiculation and formation of bullae. An important finding is a non-pitting oedema extending outside the erythematous patches. The disease often progresses and involves further skin areas proximal to the initial ones. Gangrene tends to follow in multiple sites after the 1st week of illness. Group A streptococci in conjunction with widespread thrombosis and vascular necrosis of the involved skin are two major factors in the pathogenesis of the gangrene. Early debridement and excision of necrotic tissue in combination with large doses of penicillin and cloxacillin are confirmed as mandatory to remove toxaemia and inhibit further necrosis of the skin. In 3 of the 8 patients with necrotizing fasciitis the syndrome of disseminated intravascular coagulation complicated the course of the disease. A promising therapeutic result was seen in 2 further patients exhibiting alarming signs and symptoms of early necrotizing fasciitis; the combination of heparin, given intravenously in therapeutic doses guided by activated partial thromboplastin time studies, and of systemic antibiotics alleviated the symptoms, which vanished within 10 days of the start of treatment.