The development of catecholamine-containing neurons (CA neurons) in the fruit fly Drosophila melanogaster was studied. Glyoxylic-acid-induced histofluorescence and antibodies against dopamine and tyrosine hydroxylase were used to describe catecholamine distribution in the larval central nervous system (CNS). The three techniques gave rise to a similar pattern of distribution of putative CA neurons. At all developmental stages CA neurons were distributed widely throughout the CNS but represented only a small fraction of all CNS neurons. Catecholamine-containing processes were confined to the CNS. The CA neurons are first discerned at about 18 hours of embryonic development. We suggest that these larval CA neurons are maintained throughout the ontogeny of the fly and that the adult CA pattern is composed of embryonic neurons and neurons that differentiate during metamorphosis.