Low-volume, dual-rate, continuous subcutaneous insulin infusion (CSII) creates long periods of nearnormalization of blood glucose and major intermediary metabolites in most insulin-requiring diabetic patients. The technology and strategy of the system are discussed. We have observed encouraging clinical and fluorescein angiographic improvement in severe diabetic retinopathy after 3 mo of outpatient CSII; in the kidney, glomerular capillary permeability (microalbuminuria) is reduced or normalized in long-standing diabetic patients after a few days of CSII-induced strict control. Reduction in insulin dose during CSII treatment of newly diagnosed ketonuric diabetic patients may indicate improved B-cell function in this group. Although CSII must remain a research tool, undertaken only under close medical supervision, it is increasingly likely that the technique affords the conditions for testing the hypothesis that metabolic near-normalization of diabetes slows, arrests, or reverses the course of the microvascular disease associated with the syndrome.