We have previously reported that the noradrenaline concentration in segments of the rat tail artery increases after 10-12 weeks of STZ diabetes (Morrison et al, 2004). The aim of this study was to investigate the changes in the concentration of the sympathetic postganglionic co-transmitter NPY, and the concentration of CGRP, a marker for the afferent fibres. NPY and CGRP are synthesized in the cell bodies of the sympathetic and dorsal root ganglia and are transported to the periphery of the axon, whereas noradrenaline is synthesized in the varicosities. In diabetic autonomic neuropathy is it believed that axoplasmic transport is impaired, and the experiments were performed to investigate whether transport of NPY and CGRP to the most distant nerve terminals is preferentially affected. Male rats were injected with STZ (60 mgs/kg) at 10 weeks of age, and tissues were taken from diabetic animals that had been decapitated after 12 and 16 weeks of hyperglycaemia, and were compared with the age-matched controls. The tail artery was removed and divided into three segments – proximal, middle and distal – each approximately 5 cms in length, and the peptides were extracted from these segments and stored before radioimmunoassay. The rat tail artery contains some of the longest afferent and sympathetic postganglionic neurones in the body and we have examined the concentrations of CGRP and NPY in the three segments of the artery of diabetic and control rats. In the control animals the concentration of NPY decreased from proximal to distal segments (p<0.02), whereas the CGRP concentration increased distally (p<0.0002) at 26 weeks of age. STZ-diabetes caused a fall in the concentrations of NPY and CGRP in the middle and distal segments of the tail after 12 and 16 weeks of hyperglycaemia, relative to the age-matched control rats. The results were significantly reduced in the middle segment of the artery for NPY (p<0.001) and in the distal segment for CGRP (p<0.0001) at 12 weeks; whereas at 16 weeks only the NPY level had fallen significantly (p<0.001). The results suggest that the transport of CGRP and NPY to the most distant terminals may be impaired in STZ diabetes. These results also contrast with the changes in noradrenaline concentration reported previously (Morrison et al, 2004); the differences may be explained by impaired axonal transport of peptides in STZ-diabetes .