Abstract: Expression of human prolactin in the mammary gland, one of the main target organs of this hormone, leads to the formation of an autocrine‐paracrine proliferative loop in this tissue. Involvement of prolactin in normal and neoplastic mammary development triggered the interest in transcriptional regulation of the human prolactin gene in mammary cells. Analysis of this regulation, and comparison to that in the pituitary, will contribute to a better understanding of mammary gland development and tumor formation. Here we present the first extensive analysis of the transcriptional regulation of the human prolactin gene in human mammary tumor cells.