An earlier report described cutaneous lesions, consisting of erythema with or without necrosis, on the legs and/or feet of elderly diabetics and the cause was suggested to be an altered reaction to precipitating factors such as cardiac decompensation. The present investigation concerns the cutaneous reactions to traumatization with local heat or cold to the skin of legs and forearms of 35 diabetics and 25 controls. Petechiae within the area of traumatization with either heat or cold were observed more often in diabetics than in controls. They occurred more frequently on the legs than on the forearms. Among the controls, petechiae were observed only in those over 50 years of age and only on the legs. In the diabetics under 50, petechiae were almost always observed when the duration of diabetes was 10 years or more but seldom in young patients with diabetes of short duration. The duration of diabetes was not significantly related to the occurrence of petechiae in diabetics over 50. In these diabetics, moreover, petechiae developed after traumatization with heat of a lower temperature than that which caused petechiae to appear in corresponding controls. The initial skin lesions in dermopathia diabetica (Melin) have a reddened border. The skin of the legs of some of the diabetics developed an intensely reddened border round the area of experimental heat or cold traumatization. These patients were either elderly diabetics or younger patients with diabetes of long duration. Each of them had dermopathia diabetica and each developed atrophic circumscribed skin lesions on the site of traumatization. Nineteen diabetics had dermopathia diabetica and 16 of them developed atrophic circumscribed skin lesions on the site of traumatization, lesions which were never seen in the controls. Thus, diabetics differ from controls in their reaction to a certain thermal trauma. The possible reasons for this altered reaction are discussed.