This study measured the velocity of fast orthograde axonal transport of incorporated 3H-proline in motoneurones of the sciatic nerve in control rats and in rats with streptozotocin-induced diabetes of 3 weeks duration. Sciatic nerve and abdominal cavity temperatures were monitored throughout the period of measurement of transport velocity, and the rats were warmed to minimise hypothermia at both sites. There was marked abdominal and sciatic nerve hypothermia immediately after operation, and this effect was more intense in diabetic rats than in control rats. In steady state, abdominal cavity temperature (mean +/- SEM) was 38.1 +/- 0.1 degree C in both control and diabetic rats, and the sciatic nerve temperatures were 37.8 +/- 0.1 degree C in controls and 37.1 +/- 0.3 degrees C in diabetic rats. The difference was not statistically significant. The velocities of orthograde axonal transport for the fastest molecules containing 3H-proline were 14.0 +/- 0.9 (SEM)mm/h for controls and 13.9 +/- 1.1 (SEM)mm/h for diabetic rats. Thus, no velocity difference was observed. The findings are discussed in relation to measurements of fast orthograde transport velocity in experimental diabetes in other studies. It is suggested that, where velocity deficits have been seen in diabetic rats, nerve hypothermia should be considered as a contributory factor.