To evaluate the long-term effects of near-normoglycaemia on somatosensory and autonomic nerve dysfunction, 55 poorly controlled Type 1 diabetic patients were allocated to intensified insulin treatment using continuous subcutaneous insulin infusion or multiple insulin injections and were studied prospectively for 48 months. They were divided into three groups according to their mean HbA1 levels during the study. Group 1 (n = 19) had mean HbA1 during months 3-48 in the normal range of less than 7.8% (near-normoglycaemic control), Group 2 (n = 18) showed moderately elevated mean HbA1 between 7.8 and 8.5% (satisfactory control), and Group 3 (n = 18) had clearly elevated mean HbA1 of greater than or equal to 8.6% (poor control). In the three groups studied, the changes in nerve conduction over baseline in the median and peroneal motor nerves as well as median and ulnar sensory nerves after 4 years were inversely related to the mean HbA1 levels of months 3-48 (all p less than 0.05). No significant associations with mean HbA1 were noted for the ulnar motor and sural sensory nerve conduction, vibration perception threshold, and heart rate variation. The percentages of patients with neuropathic symptoms decreased from 32 to 14% in Group 1, remained fairly constant in Group 2, and increased from 41 to 73% in Group 3 after 48 months when compared to baseline (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)