Neuroendocrine secretory protein 55 (NESP55) is a soluble, acidic and heat-stable protein, belonging to the class of chromogranins. It is expressed specifically in endocrine cells and the nervous system, and is probably involved in both constitutive and regulated secretion. In the present study, we investigated the distribution of NESP55 in various rat sympathetic ganglia by immunohistochemistry. The expression of NESP55-IR was detected in a subpopulation of principal neurons in the rat SCG, which was also TH positive, and, thus, adrenergic. In the rat stellate ganglion, more than two thirds of NESP55 positive neurons were adrenergic. Colocalization of NESP55 and calcitonin gene-related peptide (CGRP) in cholinergic neurons was also observed. In the rat thoracic chain, however, the majority of NESP55 positive neurons appeared to lack TH. No detectable NESP55-IR was found in the mouse SCG. Furthermore, in the sexually dimorphic SCG, it was demonstrated that, 80% of the NESP55 positive principal neurons were also NPY positive in the male rat, while a slightly higher, but statistically significant proportion, 87%, was found in the female. Whether or not this small difference is physiologically significant is unknown. The present data provide basic knowledge about the expression of NESP55 in the sympathetic autonomic nervous system of rat, which may further our understanding of the functional significance of NESP55.