Adipocyte-epithelial cell interactions and their secretions are critical determinants of mammary gland development. In this present study, we examined the possible involvement of leptin and its receptors in the process of mammogenesis/lactogenesis. We demonstrated by reverse transcription and polymerase chain reaction analysis that long and short forms of leptin receptors were expressed in the ovine mammary gland during pregnancy and lactation. Furthermore, quantitative determinations, via ribonuclease protection assays, provided evidence that the level of leptin receptor expression was greatest during mid-pregnancy when active growth of the mammary gland is initiated. Location of the leptin receptors, as determined by in situ hybridization analysis, revealed that leptin receptor transcripts were expressed specifically in mammary epithelial cells. These data provide evidence that leptin, with its receptors, could be an important mediator in regulating mammary gland growth and development.