AbstractThe aim of this study was to investigate the possibility of enhancing the yield of tissue plasminogen activator (tPA) from two epithelial cell lines of normal (non‐malignant) derivation grown in tissue culture. The three agents used in this investigation were chosen because of thier proven enhancing effect on analogous cells or products. The anabolic hormone stanozolol was found to have no significant stimulatory effect on these cell lines. A phorbol acetate (12‐O‐tetradecanoylphorbol 13‐acetate) caused a twofold enhancement in tPA yield but the most significant results were obtained with 5‐azacytidine. This agent increased the yield by up to fourfold in small stationary cultures and threefold in large‐scale microcarier cultures. A combination of azacytidine and phorbol acetate did not have an additive effect on total yield but did alter the kinetics of tPA expression with time. Indications were that the maximum yield with these types of potentiating agents was achieved as it could not be increased by using a combination of two diffe