Intracellular recording and labelling with Lucifer yellow of respiratory neurons in the rostral ventrolateral medulla were carried out in urethane-anaesthetised rats. A combined immunofluorescence and immunoperoxidase technique enabled an assessment of the tyrosine hydroxylase immunoreactivity, as well as an examination of the morphology of inspiratory and expiratory neurons in this part of the medulla oblongata. The results demonstrate: a) that respiratory neurons in the rostral ventrolateral medulla of the rat are intermingled with catecholamine-containing neurons of the C1 cell group, but are not themselves catecholamine-containing; b) that many non-spinally projecting respiratory neurons have axonal arborisations within the ventrolateral medulla in the same region as the C1 cell group, other respiratory neurons, and neurons reported to have a cardiovascular function; and c) that the dendrites of respiratory neurons in this region radiate throughout the ventrolateral medulla and frequently approach the ventral surface.