Dopamine is one of a number of neurotransmitter candidates found in the insect CNS, It has been localised in a number of neurones, and others have been shown to respond to the application of dopamine. This study investigates the response of the common inhibitory motoneurone D3 to dopamine, and its ionic basis. The response to dopamine is distinguished pharmacologically from responses to noradrenaline, octopamlne and acetylcholine, all neurotransmitter candidates within the insect CNS, and it is concluded that a receptor specific for dopamine is present on this cell. Finally, this putative dopamine receptor is characterised pharmacologically, and its position relative to the extant classification schemes for mammalian receptors, and its similarity or otherwise to other invertebrate dopamine receptors is discussed.