Abstract: Serum prolactin concentrations were mersured in 195 mammary neoplasias, the women with fihoadenoma. hyperplasis (except for one-side light degree hyperplasia) and carcinoma of the breast at the Ⅱ、Ⅲ、Ⅳ period had significantly higher prolactin levels than control subjects (P0. 01). Prolaelin levels of the patients With breast cancer increased remarkably with developmet of the disease (P0.01). These results suggested prolactin proboly promoted the growth of the breast tumour.