The effects of strict blood glucose control on total skin blood flow and capillary blood flow velocity in finger nailfold capillaries were assessed in nine diabetics. Measurements were made before (blood glucose: 11.2 +/- 0.8 mmol/l) and after nine days of continuous subcutaneous insulin infusion (CSII) (blood glucose 6.2 +/- 0.8 mmol/l, p less than 0.001). Resting finger skin blood flow, measured by venous occlusion plethysmography, was 18.6 +/- 2.7 ml/100 ml tissue/min before and 12.6 +/- 2.7 ml/100 ml/min (ns) after CSII. Nailfold capillary red cell velocity, measured by television video microscopy, rose significantly from 0.36 +/- 0.09 mm/s before to 0.71 +/- 0.14 mm/s (p less than 0.01) after CSII. Venous oxygen tension, measured in samples of blood taken from an antecubital vein, tended to fall after CSII (from 6.1 +/- 0.4 kPa to 4.6 +/- 0.5 kPa/ns). No change was seen in whole blood viscosity, plasma viscosity or red cell filtration rate during the study although heart rate fell from 81.3 +/- 2.0 to 75.2 +/- 1.7 beats/min (p less than 0.02). The results suggest that there is a redistribution of skin blood flow following improved diabetic control which favours the nutritive microcirculation.