By using a double immunofluorescence method we examined the distribution of noradrenergic neurons expressing substance P receptor (NK1) or neuromedin K receptor (NK3) in the rat brainstem. The distribution of SPR-like immunoreactive (-LI) neurons completely overlapped that of tyrosine hydroxylase (TH)-LI neurons in the locus coeruleus (A6), ventrolateral and lateral reticular formation of pons (A5 and A7). Partially overlapping distribution of SPR- and TH-LI neurons were found in certain regions of the medulla oblongata (A1-A4). Neurons showing both SPR- and TH-like immunoreactivities, however, were only found in the locus coeruleus complex (A5-A7): 100% of these TH-LI neurons displayed SPR-like immunoreactivity. Neurons showing both NKR- and TH-like immunoreactivities were not detected in the aforementioned areas of brainstem. The present study has provided morphological evidence for direct physiological modulation of noradrenergic neurons by tachykinins through SPR in locus coeruleus complex (A5-A7).