Enzymes of intermediary metabolism were assayed in seven tissues (liver, kidney, rectal gland, white muscle, red muscle, heart and brain) of the little skate, Raja erinacea, to assess the general metabolic design of these tissues. Judged b,y the activities of enzymes linked to oxidative processes, the kidney, red and heart muscles, and rectal gland are the most metabolically active tissues, with ketone bodies potentially supplying the bulk of the required energy. The brain is the only tissue with substantial potential to utilize exogenous glucose as a n oxidative substrate; it also has the capacity to synthesize and degrade glycogen. The rectal gland may also use exogenous glucose, although its glycolytic potential is minor compared to that of other tissues. Amino acids, in addition to ketone bodies, may play a significant metabolic role in these oxidative tissues based on the tissue activities of the amino transferases and the plasma content of amino acids. Enzyme activities in white skeletal muscle reflect the benthic, sluggish lifestyle of this species with low oxidative potential and rather limited anaerobic capacity. Hepatic tissue appears to be designed Sor the export of ketone bodies and to display a high potential for amino acid metabolism. The potential for gluconeogenesis, albeit