Vasoactive intestinal peptide (VIP) has recently been detected in rat ovaries and has been shown to stimulate steroidogenesis by cultured rat granulosa cells. In this study we investigated whether the VIP-messenger RNA (mRNA) can be detected in the ovaries, thus suggesting local synthesis of the peptide. To study VIP-gene expression, a sensitive RNA detection assay which uses in vitro transcribed RNA probes corresponding to specific exons of the VIP gene was developed. Using this method, an approximately 2000-base RNA band containing the coding sequences for VIP was detected in rat ovaries. This RNA also contains the coding sequences for the VIP-related peptide (peptide-histidine-methionine). An identical VlP-encoding RNA was previously identified in the rat cerebral cortex. However, the VIP-mRNA quantity in the cortex was 12-foldhigher as compared to the ovaries. These results may reflect the differences in VIP concentration in the two organs. The finding of VIP-encoding mRNA in the rat ovaries suggests a local synthesis of VIP in the ovaries.