The accurate replication in vitro of bovine mammary gland function would be of enormous benefit to studies investigating the control of milk synthesis and secretion. However, progress towards this end has been slow, partially because of the biological variability in the cell preparations produced to date. In particular, the heterogeneous nature of primary cultures of mammary epithelial cells (MEC) makes them unstable for repeated experimentation over time, while for immortalised cell lines in vitro the level of milk protein production is either very low or non existent; if it does occur it has been independent of in vivo factors known to regulate mammary growth and milk secretion. The aim of this project was to establish a bovine MEC non-immortal clone, which is both responsive to mitogens and functionally responsive to lactogenic hormones and an appropriate extracellular matrix.