Arvicolinae voles are small herbivores relying on constant food availability with weak adaptations to tolerate prolonged food deprivation. The present study performed a comparative analysis on the responses to 4-18 h of food deprivation in the common vole (Microtus arvalis) and the tundra vole (Microtus oeconomus). Both species exhibited rapid decreases in the plasma and liver carbohydrate concentrations during phase I of fasting and the decline in the liver glycogen level was more pronounced in the tundra vole. The plasma thyroxine concentrations of the common vole decreased after 4 h. Lipid mobilization (phase II of fasting) was indicated by the increased plasma free fatty acid levels after 8-18 (the common vole) or 4-18 h (the tundra vole) and by the elevated lipase activities. In the tundra vole, the plasma ghrelin concentrations increased after 12 h possibly to stimulate appetite. Both species showed increased liver lipid concentrations after 4 h and plasma aminotransferase and creatine kinase activities after 12-18 h of food deprivation implying liver dysfunction and skeletal muscle damage. No signs of stimulated protein catabolism characteristic to phase III of fasting were present during 18 h without food.