Ten patients with insulin-dependent diabetes mellitus (IDDM) had fundus photographs and fluorescein angiograms obtained before and after a control period characterized by conventional insulin injections and a test period characterized by continuous subcutaneous insulin infusion (CSII). The mean glycosylated hemoglobin value at the end of the control period was 14.3% +/- 3.8% and decreased to 10.1% +/- 3.3% at the end of the test period. During the control period, none of the patients' eyes changed more than one grade in a modified Early Treatment Diabetic Retinopathy Study classification. All seven eyes without retinopathy at the start of the control period were still without retinopathy at its completion. One eye improved three grades during the test period, but four eyes, including two without retinopathy when CSII was initiated, progressed one grade. The data suggest that metabolic control that is improved but not normalized by CSII neither reverses retinopathy in IDDM nor prevents its development.