We demonstrate that blockage of EGF receptor signal transduction is sufficient by itself to cause a rapid, efficient, and reversible G0-like growth arrest of normal human mammary epithelial cells (HMEC) of finite lifespan as well as two immortally transformed cell lines derived from normal HMEC following in vitro transformation with benzo[a]pyrene. For normal HMEC, the significant level of endogenous production of TGF alpha requires utilization of blocking antibodies to the EGF receptor to achieve cessation of growth in mass culture, whereas removal of EGF is sufficient to arrest the immortal cell lines. In the growth-arrested cells, protein synthesis remains depressed; reexposure to EGF leads to a rapid increase in protein synthesis. Inhibition of DNA synthesis is not detectable until approximately 12 h after removal of EGF/TGF alpha and is pronounced by 24 h. Reexposure to EGF produces high levels of synthesis of the early response genes, c-myc, c-fos, c-jun, and MGSA, within 1 h. DNA synthesis increases only after 10 h, with a sharp peak after 15-20 h. Reexposure of the growth-arrested normal HMEC for 1 h with EGF allows a majority of the cells capable of cycling to subsequently enter the S phase. Little is currently known about cell cycle control in normal human epithelial cells. The efficient and gentle method of achieving reversible G0 growth arrest reported here may facilitate studies on the cell cycle of this cell type. Additionally, results from normal HMEC can be compared with those from syngeneic immortalized cell populations to determine possible cell cycle parameters altered as a result of immortal transformation.