To test the hypothesis that repeated loss and gain of weight through dieting will result in increasing fatness, 200-g female Sprague-Dawley rats were castrated and allowed to become obese on a high-fat diet for 6 wk. Two successive periods of severe food restriction (50% maintenance for 28 d and 25% maintenance for 21 d) were each followed by ad libitum refeeding on the high-fat diet until control body weights were attained. Percent body fat was determined indirectly from body density and total-body water at the end of each cycle. Restricted rats gained weight and attained control body weights on ad libitum feeding without overshooting these weights, and percentage body fat was not different from that of controls at the end of either cycle (cycle 1 22.3 +/- 1.7 vs 23.8 +/- 1.7%; cycle 2 19.0 +/- 1.1 vs 21.6 +/- 0.8%). Repeated cycles of weight loss and regain do not produce increased body fatness or decreased rate of weight loss in ovariectomized rats.