We have shown that serum, fibroblast growth factor, epidermal growth factor, and the tumour promotor, 12-O-tetradecanoylphorbol- 13-acetate (TPA), selectively induce the synthesis of certain secreted proteins in a variety of cell types. Similarly, a specific growth inhibitor protein selectively induces the synthesis of a secreted protein that is different from those induced by growth factors. In each case, the average increase in labeling by [3%]methionine of these secreted proteins after their induction is 7- to 10-fold. No correspondingly large increase is detected for intracellular proteins.