Abstract A sensitive sucrose gradient procedure provided evidence for specific 3.6S 1,25-dihydroxyvitamin D 3 [1,25(OH) 2D 3] receptor-like binding components with low affinity for 25(OH)D 3 in several reproductive target tissues in the rat, inclucling testis, uterus and probably epididymis. Thus, the presence of 1,25(OH) 2D 3 receptors in non-vitamin D endocrine tissues is not restricted to the hormone secreting glands. Estrogen-stimulated uterine growth paralleled increased levels of the putative 1,25(OH) 2D 3 receptors, provicling in vivo evidence for the concept of a relationship between these phenomena. However, a similar correlation was not observed in the growing testis (prepubertal vs mature rats). Whether this result stems from receptor localization in a cell type prevalent in the adult or a true dissociation between testis growth and receptor levels is unclear. Finally, significant levels (10.3 ± 1.0% vs intestinal mucosa) of the putative 1,25(OH) 2D 3 receptors were found in the heart, an organ in which calcium mediates many specialized functions. Taken collectively, these observations on new target tissues of quite different overall function suggest that 1,25(OH) 2D 3 and its receptors may play a role in intracellular calcium homeostasis and possibly in regulating specialized intracellular functions of calcium.