Hormonal, metabolic and cardiovascular responses to insulin induced hypoglycaemia were investigated in seven Type 1 (insulin-dependent) diabetic patients with residual B cell function, eight Type 1 diabetic patients without B cell function and six healthy subjects. No differences were found between the diabetic groups regarding nadir of glucose and rate of recovery to normoglycaemia. The patients with residual B cell function had a glucagon response to hypoglycaemia which was close to that of normal subjects. In patients without B cell function, the glucagon response to hypoglycaemia was present, albeit significantly smaller than in the patients with preserved B cell function (0.025 ng/ml, range 0.007–0.042 versus 0.054 ng/ml, range 0.029–0.087). The group without B cell function had signs of an exaggerated rate of lipolysis and ketogenesis compared with the patients with B cell function and the normal subjects.