Ten to 20 days after starting prophylactic doses of heparin in six patients, large, indurated, erythematous plaques appeared at the sites of the subcutaneous injections. Pruritus, local tenderness, and burning sensation or pain were present. No skin necrosis developed. Heparin was discontinued and topical corticosteroids were applied to the involved areas. Five to 9 days later the lesions had resolved completely. The reaction seen in the six patients is similar to the early erythematous phase of the so-called heparin necrosis. There is a spectrum of cutaneous changes ranging from mild erythematous pruritic areas to large symptomatic plaques and to heparin necrosis, following subcutaneous injections of heparin.