Exponentially growing DD-1 cells (differentiation-defective cells) synthesize prostaglandins, while exponentially growing MyoDD-1 cells (differentiation-competent cells; DD-1 cells transfected with the myogenic regulatory gene MyoD) synthesize little or no prostaglandins and have reduced levels of prostaglandin H synthase-1 RNA [J. R. Wolf et al., 1993, Exp. Cell Res. 207, 439]. However, MyoDD-1 cells have the capability of synthesizing prostaglandins in response to serum stimulation of serum-deprived cells. The serum stimulation of prostaglandin biosynthesis is associated with transient increases in both prostaglandin H synthase-2 RNA and protein. DD-1 cells and MyoDD-1 cells are similar with respect to prostaglandin biosynthesis and expression of prostaglandin H synthase-2 following serum stimulation of serum-deprived cells. In contrast, the expression of prostaglandin H synthase-1 is higher in DD-1 cells as compared to MyoDD-1 cells under all culture conditions. Thus, expression of myogenic regulatory genes is associated with the differential regulation of prostaglandin H synthase-1 and prostaglandin H synthase-2.