30 insulin-dependent diabetic patients with background retinopathy were randomised to conventional treatment (UCT) or treatment with continuous subcutaneous insulin infusion (CSII). They were followed prospectively for 1 year with fortnightly seven-sample home blood glucose measurements and retinal examinations every 6 months. Mean blood glucose and stable haemoglobin A1c during months 3-12 were significantly lower in the CSII than the UCT group. Retinal morphology deteriorated during the year with no significant differences between UCT and CSII groups. The frequency of deterioration was highest in the CSII group, especially among the 10 patients with best glycaemic control. Proliferative retinopathy developed in 3 patients--2 of these were CSII treated. Retinal function (oscillatory potential, macular recovery time, and posterior vitreous fluorophotometry) improved significantly with CSII treatment and deteriorated significantly with UCT. Changes in retinal function were most pronounced in patients with the best and the poorest regulated glycaemic control.