The effects of food restriction (50% of ad libitum-fed controls) on maternal tissues during lactation (LR) or during both gestation and lactation (GLR) were examined in rats. Skeletal muscle protein, RNA and fiber diameter were reduced in response to the LR and GLR treatments, but muscle DNA and fiber number were unchanged. Mean body weights of the pregnant (GLR) and nonpregnant female rats were not significantly different after the first 3 wk of food restriction (after delivery in pregnant GLR rats). Compared to the controls, pups of the GLR females had a significantly smaller mean birth weight. The LR females lost weight and catabolized fat pads, organs, and skeletal muscles while nonlactating females gained weight when given a similar amount of food. These results indicated that the demands of gestation did not significantly add to the loss of maternal body weight due to the restriction of food intake. However, the demands of lactation caused the food-restricted females to catabolize significant amounts of maternal tissues.