Dorsal root ganglion (DRG) sensory neurones are depolarised by the excitotoxin capsaicin. This ability to respond to capsaicin is dependent on nerve growth factor (NGF) in dissociated, cultured, adult rat DRG neurones. We tested the ability of NGF (50 ng/ml) to regulate capsaicin sensitivity in a different group of sensory neurones, namely those of the vagal ganglia. Capsaicin sensitivity, measured in populations of neurones by capsaicin-evoked 45Ca uptake, or in single neurones using a cobalt staining method, was apparent in vagal ganglion neurones after 1 day in culture, but after 5 days in the presence or the absence of NGF, capsaicin-stimulated 45Ca uptake was essentially abolished. As some vagal ganglion neurones exhibit responses to brain derived neurotrophic factor (BDNF), we grew cells in BDNF (1 microg/ml) and found that the capsaicin sensitivity was now apparent at 5 days. Therefore BDNF but not NGF, regulates capsaicin sensitivity in adult rat vagal ganglion neurone cultures. BDNF cannot, however, substitute for NGF in DRG neurone cultures.