The possibility that glycosylated haemoglobin levels and/or blood pressure might correlate with cardiac sympathetic neuropathy and/or diabetic somatic neuropathy was investigated in patients with non-insulin-dependent diabetes mellitus. Sympathetic nerve function was quantified by analysis of [123I]metaiodobenzylguanidine accumulation in the cardiac muscle. Somatic nerve function was assessed by measuring the motor nerve conduction velocities of the peroneal and tibial nerves, and the sensory nerve conduction velocity of the sural nerve. None of the parameters of cardiac sympathetic neuropathy or diabetic somatic neuropathy showed any correlation with blood pressure, nor was there any evidence of a correlation between cardiac sympathetic neuropathy and glycosylated haemoglobin levels; there was, however, a significant correlation between diabetic somatic neuropathy (as indicated by tibial nerve conduction velocity) and glycosylated haemoglobin levels. The results are consistent with the view that different mechanisms are involved in the two types of neuropathies.