The adjustment of seven rats to 35 days of 23-hr. food deprivation cycles was measured in terms of body weight, food and water intake, 24-hr. activity (revolving wheel), and activity during the last pre-feeding hour. Comparison with a control group reveals that progressive changes in all measures continued for the first 15 days at least, and that activity during the hour immediately prior to feeding was still increasing at the end of the 35 days. It is possible that similar trends constitute an unrecognized source of error in other experiments involving daily feeding cycles.