Retrograde tracing with True Blue was combined with immunocytochemistry to determine the source of any calretinin-immunoreactive (CR-ir) nerves projecting to the rat ovary. In the ovary, a strong signal for calretinin immunoreactivity was localized in interstitial gland cells; however, no intraovarian CR-ir nerves could be demonstrated. When the superior ovarian nerve was isolated, cut, and True Blue applied to the proximal end, the fluorescent dye was retrogradely transported to a population of cells located in T-12, T-13, and L-1 dorsal root and paravertebral ganglia. There was virtually no dual labeling of cells in these ganglia with calretinin (< 0.009% dual labeling in dorsal root and <0.014% in paravertebral ganglia). However, greater than two-thirds of the True Blue-labeled cells were immediately adjacent to CR-ir cells in dorsal root ganglia. This arrangement is suggestive of a paracrine mechanism between CR-ir cells and cells projecting to the ovary. In paravertebral ganglia, 63% of cells projecting to the ovary were surrounded completely or partially by beaded CR-ir nerve fibers. The source of these fibers (sensory or preganglionic sympathetic) is unknown but hypothesized to be preganglionic. Collectively, these observations suggest a participatory role for calretinin in ovarian function, either directly via effects on the interstitial gland or indirectly by influencing neurons projecting to the ovary.