Two doses of epinephrine were infused for 6 hr into isolated catfish liver previously perfused with a glucose-free medium or with a medium containing 10 mM glucose. The hormone induced (a) a continuous decrease in liver glycogen level, both in absence and in presence of glucose in the medium; low dose of epinephrine was without effect on the decay of glycogen; (b) a great release of glucose, both in absence and in presence of glucose in the medium; the low dose of epinephrine induced an effect similar to the maximal dose, only in experiments without glucose in the medium; (c) no effect on lactate uptake by liver; or (d) a prevention of the decline in liver glycogen phosphorylase activity observed during 1 hr incubation of liver slices. It has been concluded that epinephrine caused an increase of glucose in perfusion medium with different mechanisms according to the level of glucose and the dose of epinephrine. High doses of hormone cause the glycogenolysis by activation of glycogen phosphorylase, both in presence and in absence of glucose; low doses of epinephrine probably preferentially promote in liver the gluconeogenetic processes in glucose-free experiments.