Pro-vasopressin mRNA, neurophysin and arginine vasopressin (AVP) were assayed in the mouse anterior pituitary gland, in mouse anterior pituitary cells in culture and in the AtT-20 corticotrophic tumour cell line. Northern blot analysis revealed the presence of an ∼700 base pair pro-vasopressin mRNA in anterior pituitary and AtT-20 cells. Neurophysin, identified by immunoblots, and AVP, identified by high-performance liquid chromatography and cross-reactivity with AVP antiserum, were detected in anterior pituitary cells and AtT-20 cells. Immunocytochemical staining with anti-neurophysin showed that ∼40–45% of the dissociated anterior pituitary cells in culture and >95% of the AtT-20 cells were stained. Anterior pituitary cells in culture and AtT-20 cells had a basal level of release of AVP in the 0·01–0·1 nm range. These results indicate that anterior pituitary cells and AtT-20 cells have the ability to synthesize and process pro-vasopressin to AVP and neurophysin, endogenously.