There is now overwhelming evidence--radio-immunoassay, immunofluorescence, Northern blot analysis with highly specific cDNA probes--for the production of vasopressin and its congeners in the rat ovary as well as the hypothalamus. Ontogeny studies and studies over the oestrous cycle suggest that such production is controlled by different mechanisms in the two tissues. Studies in Brattleboro rats suggest that the production of vasopressin and its congeners involves different post-transcriptional mechanisms in these tissues. In Brattleboro rats hypothalamic mRNA is either not translated, or yields a very short-lived product, whereas ovarian levels of immunoreactive vasopressin are indistinguishable from those in control animals. The mechanism of this tissue specificity, and its implications in terms of potential paracrine roles for vasopressin and, or its congeners awaits explanation.