The technique of steroid hormone autoradiography has been used to study the cellular distribution of ecdysteroid binding sites in the ventral nervous system of the tobacco hornworm moth, Manduca sexta. The ligand was 26-[125I]iodoponasterone. Tissue was examined from the subesophageal ganglia, thoracic ganglia, and abdominal ganglia of larvae at two times during the larval-pupal transient: the 2nd day of wandering and the prepupal stage. The patterns of neuronal binding seen were compared with those found in earlier autoradiographic studies of hormone binding in tissue sampled on the 1st day of wandering, in the pharate adult, and in the 4-day-old moth (Fahrbach and Truman, '89). The pattern of binding was reproducible but dependent upon developmental stage: whereas only a subset of neurons exhibited nuclear accumulation of radiolabeled ecdysteroids on the 1st day of wandering, less than 24 hours later nearly every neuron in the ventral nervous system was labeled. A limited pattern of binding, however, was seen again in the prepupal nervous system. Thus, the insect nervous system is able to use a single hormone both as a general cue for metamorphic development and as a single targeted to stage-specific subsets of neurons by alternating periods of ubiquitous expression of receptor with periods during which the capacity to bind the steroid hormone is highly restricted.