"Essential labile diabetes" is an insulin-dependent diabetes, in the course of which irregular and unpredictable hyperglycemias, frequently with ketosis, and sometimes serious hypoglycemias alternate. In spite of careful treatment with insulin, diet and suitable hygienic measures, this form of diabetes cannot be influenced. Fortunately, it seldom occurs, not more frequently than in 1 to 2% of diabetics. Various attempts have been made to explain the pathogenesis of this form of the disease. The most probable explanation is that there is an almost complete exhaustion of insulin secretion. This hypothesis is based on the extremely low level of the C peptide below 0.60 ng/ml, whereas in non-labile insulin-dependent diabetics the C peptide amounts to more than 2.2 ng/ml