1. Intracellular recordings have been made of the hyperpolarization of cockroach salivary gland cells induced by nerve stimulation and dopamine. 2. The relative potency of a number of dopamine antagonists in inhibiting the dopamine- and nerve-mediated hyperpolarization was studied. SCH23390 (10-50 microM), chlorpromazine (0.1-5 microM), haloperidol (10-100 microM) and metoclopramide (1 mM) inhibited the hyperpolarization. 3. In contrast, domperidone and (+/-)-sulpiride potentiated the hyperpolarization induced by both nerve stimulation and dopamine. 4. Apparent dissociation constants (KDapp) were obtained for the blockade of the dopamine-induced hyperpolarization. The rank order of potency (KDapp in parentheses) was as follows: chlorpromazine (0.2 microM); haloperidol (3.3 microM); SCH23390 (4.1 microM); metoclopramide (265 microM); domperidone and (+/-)-sulpiride (inactive). 5. It is concluded that the receptor subserving the dopamine-induced hyperpolarization of the salivary gland acinar cells is the same as that mediating the secretory response to dopamine. In addition these data support our findings, which suggested that this receptor is similar to the D1 dopamine receptor, but distinct from the D2 receptor found in mammalian systems.