The effect of 6 months of strict metabolic control upon eye and kidney function was studied in 32 insulin-dependent diabetics randomised either to unchanged conventional treatment (UCT) or to continuous subcutaneous insulin infusion (CSII). Retinal function was assessed by means of the macular recovery time (measured with nyctometry), the oscillatory potential (measured with electroretinography), and fluorophotometry. Renal function was assessed by the glomerular filtration rate (GFR) and the urinary albumin excretion rate. Individual median blood-glucose levels during the 6 months were 9.2 +/- 2.0 mmol/l (mean +/- SD) in the UCT group and 5.6 +/- 0.7 mmol/l in the CSII group. Haemoglobin Alc fell from 8.8 +/- 1.2 to 8.0 +/- 2% in the UCT group and from 9.6 +/- 1.7 to 6.7 +/- 1.0% in the CSII group. The UCT group showed a significant deterioration in all indices of retinal function (macular recovery -6%, oscillatory potential -5%, fluorophotometry +9%, whereas patients treated with CSII showed a distinct improvement (macular recovery +5%, oscillatory potential +7%, fluorophotometry -7%). GFR fell by 9% with CSII and rose 2% with UCT. Urinary albumin excretion fell by 12% with CSII and rose by 56% with UCT. This interim report of a one-year study supports the view that long-term control achieving near-normal blood-glucose levels may arrest or even reverse some of the features associated with diabetic microangiopathy.