We examined the potential for some of the abnormalities of vascular endothelium found in diabetes mellitus to cause neuropathic changes. Non-diabetic rats were treated for 2 months with the cyclo-oxygenase inhibitor flurbiprofen (5 mg.kg-1.day-1) to reduce prostacyclin production, the nitric oxide synthase inhibitor NG-nitro-L-arginine (5 or 25 mg.kg-1.day-1), or combined treatment. There were dose-dependent reductions in sciatic motor and saphenous sensory conduction velocity. The two inhibitors acted synergistically, thus, the 5-6% motor conduction deficits (p < 0.01) produced by either flurbiprofen or NG-nitro-L-arginine (5 mg.kg-1.day-1) increased to 17% (p < 0.001) for combined treatment. With NG-nitro-L-arginine (25 mg.kg-1.day-1) and flurbiprofen, motor and sensory conduction velocity were reduced by 23% (p < 0.001) and 12% (p < 0.001), respectively, matching the deficits following 2-month streptozotocin diabetes. NG-nitro-L-arginine (25 mg.kg-1.day-1) and flurbiprofen together produced a 13% prolongation of the time taken for 80% hypoxic conduction failure in vitro (p < 0.05) and a 10% reduction in sciatic capillary density. A second investigation tested an alternative hypothesis that overproduction of nitric oxide was responsible for vascular-related complications in diabetes, the prediction being that NG-nitro-L-arginine (5 mg.kg-1.day-1) would prevent nerve dysfunction. However, rather than prophylaxis during 2-month streptozotocin diabetes, treatment exacerbated nerve abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)