Current theories on the pathogenesis of diabetic microangiopathy and their effective therapeutical implications are reviewed. The possible role of insulin antibody production in insulin-treated diabetics concerning development and progression of retinopathy is particularly discussed. Thus the opportunity of a monocomponent (MC) insulin treatment in all newly diagnosed insulin-dependent diabetics is considered. The authors have carried out fluorescein angiography in two groups of subjects with JOD comparable for age, sex, diabetes duration (5-7 years), insulin requirement, metabolic control, absence of diabetic heredity as well as of clinical (ophtalmoscopic) signs of microangiopathy (retinopathy). The first group had been treated from the beginning with MC porcine insulin (Monotard) only; the second one with conventional Lente only. Early fluoroangiographic signs of retinopathy ("pre-retinopathy") as increased capillary filling, ischaemic areas, alterations in capillary permeability, microangioaneurysms, "primary exudation" had to be detected. In 2 out of 10 cases in the first group one isolated sign was found; one or more signs were found in the second group. In the first group the insulin antibody titer (IB) was under or nearly above the detection limit; in the second group insulin antibody titer was significantly positive. These preliminary findings suggest a larger prospective study.