We sought to examine the changes in the strength-duration time constant (SDTC) of the median nerve in diabetic polyneuropathy. The SDTC is a measure of axonal excitability and depends on the biophysical properties of the axonal membrane. It may provide some information about Na+ channel functioning. Forty-nine diabetic patients (30 men, 19 women; mean age, 54.6 +/- 9.4 years) and 15 age-matched healthy subjects (11 men, 4 women; mean age, 53.1 +/- 7.6 years) participated in the study. SDTC and rheobase values were 384.5 +/- 97.9 mu s and 4.6 +/- 2.4 mA in patients and 313.8 +/- 46.7 mu s and 6.0 2.6 mA in controls. The SDTC was found to be significantly different between the two groups (P = .009 for SDTC and P = .066 for rheobase). Fasting glucose and HbA1c levels of patients were 206.6 +/- 88.7 mg/dL and 8.8 +/- 2.4%, and these were not correlated with SDTC or rheobase (P < .05). We suggest that longer SDTC, indicating increased axonal excitability may develop in patients with polyneuropathy associated with uncontrolled diabetes. (C) 2007 Elsevier Ireland Ltd. All rights reserved.