A patient with heterozygous protein S deficiency experienced cutaneous necrosis following subcutaneous heparin administration. Deficiencies of both protein C and protein S, known risk factors for the more frequently encountered coumarin necrosis, may predispose patients to this complication of heparin therapy as well. The putative association of protein S deficiency with cutaneous heparin necrosis could not be proven, however, since attempts to reproduce the heparin necrosis were unsuccessful.