Glucose-6-phosphatase levels were measured in livers and kidneys of control mice and mice fasted for 24, 48, and 72 h, respectively. The enzyme was assayed with and without deoxycholate supplementation. When assayed in the absence of deoxycholate, significant increases in liver enzyme levels was observed after fasting for 48 and 72 h, respectively. For the kidney enzyme, a significant increase was observed only after 48 h fasting. When the enzyme was assayed in the presence of 4.8 mmol/1 deoxycholate, fasting-induced increases of liver enzyme levels were further potentiated, but no significant differences were observed in kidney enzyme levels between fasted and control mice.