During experiments directed at defining the role of various hormones in the regulation of the rat liver enzyme, serine dehydratase, it was observed that epinephrine inhibited the increase in enzyme activity normally attained following glucagon administration. Epinephrine was effective in inhibiting the normal glucagon induction when administered 1 hr before, 2 hr after or simultaneously with glucagon. Epinephrine did not inhibit the hydrocortisone induction of serine dehydratase. High doses of isoproterenol significantly decreased the high levels of serine dehydratase normally present in livers of diabetic rats and rats maintained on a high protein diet. The level of cAMP in the livers of rats receiving glucagon plus epinephrine was elevated over control values at time points between 5 and 20 min but was lower than the level in animals receiving only glucagon which remained elevated until at least 60 min after injection. Thus it is suggested that epinephrine antagonizes the normal glucagon stimulated induction of serine dehydratase via a mechanism which prevents the normal accumulation of cAMP. (Endocrinology93: 469, 1973)