This study measured the velocity of the fast anterograde axonal transport of [3H]-proline-labelled proteins in sciatic motoneurones of rats with streptozotocin diabetes of 12 weeks duration and in age matched controls. Four groups of diabetic animals were studied. One of these groups remained untreated whilst 2 diabetic groups received a long-acting insulin twice weekly to limit body wasting, but to permit regular hyperglycaemia. One insulin-treated group and one other diabetic group received an aldose reductase inhibitor, "Statil" (ICI 128436) by dietary admixture. Neither diabetes alone nor any of the treatment regimes produced any significant alteration of axonal transport velocity. Sciatic nerve temperature was measured concomitantly. A slight nerve hypothermia was seen in the untreated diabetic rats, but not in either insulin-treated group. It is concluded that 2 aspects of diabetes mellitus, namely persistent hyperglycaemia and polyol pathway activity in nervous tissue are without effect on the velocity of fast orthograde axonal transport of proteins.