Comparable groups of type I diabetic patients (n = 19) were matched for age, duration of diabetes, mean HbA1 values, insulin requirements, degree of neuropathy, and the mean of nerve conduction velocities (CV) in median, ulnar, and peroneal motor and median, ulnar, and sural sensory nerves. One group (n = 9) was managed with continuous subcutaneous infusion of (regular) insulin (CSII); the other (n = 10) with split-mixed injections of (intermediate and regular) insulin (SMII). After 12 months, glucose regulation was equally and significantly improved in both groups (P less than 0.005), although it was not sufficiently intense to normalize mean total glycosylated hemoglobin values in either group. Furthermore treatment produced no difference between groups in the values for mean amplitude of glycemic excursions, 12 month average of consecutive M-values or in clinical evaluation. However, in the CSII group, mean CV had increased 6.4% (2.75 + 0.56 m/s; mean +/- SEM) versus 1.3% (0.57 +/- 0.54 m/s) in the SMII group (P less than 0.005). Multivariate analysis on a nerve-by-nerve basis found significantly improved conduction in 2/6 nerves (median motor; ulnar sensory) in the CSII group compared to the SMII group. These results suggest that CSII may provide a more favorable microenvironment for nerve repair.