The clinical role of insulin-antibody formation, with reference to the monocomponent insulin treatment (MC), is discussed in a series of diabetological conditions. On the basis of a five-year-experience, personal results with a MC Lente treatment are presented in 32 cases of juvenile diabetes subdivided as follows: 3 cases with insulin allergy, 5 cases with insulin lipoatrophy, 13 cases with high insulin requirement, 4 cases with brittle diabetes, 7 cases with diabetic microangiopathy (retinal and, or renal). The circulating antibody level was estimated by IgG-Insulin-Binding Capacity (IB), according to Christiansen. After transfer from conventional to MC insulin treatment it was observed: -- disappearance of allergy and total remission of lipoatrophy, in parallel with a reduction of IB titer; -- decrease in insulin requirement and stabilisation of labile diabetic control, not always in concomitance with IB reduction; -- deterioration of advanced diabetic retinopathy and, or nephropathy in spite of IB reduction. It is concluded that MC insulin constitutes a major tool in the treatment of the above mentioned diabetic conditions, except for advanced microangiopathy. Thus a MC insulin treatment should be started, as a rule, in newly diagnosed diabetics, to possibly prevent such complications. However further development of insulin purification techniques, with removal of residual pro-insulin antigenic sites, is to be considered.