Male Brown Norway rats aged 4 mo (young) and 20 mo (old) received a series of experimental challenges to body fluid homeostasis over approximately 3 mo. Water was available for drinking in some tests and both water and 0.3 M NaCl were available in others. The series included 3 episodes of extracellular fluid depletion (i.e., furosemide plus 20-h sodium restriction), 2 tests involving intracellular fluid depletion (i.e., sc hypertonic saline, 2 ml/kg bw of 1M or 2M NaCl), 1 test involving overnight food and fluid restriction, and testing with captopril adulteration of the drinking water (0.1 mg/ml) for several days. Old rats were significantly heavier than young rats throughout testing. Old rats drank less water and 0.3 M NaCl following sodium deprivation than young rats, both in terms of absolute intakes and bw-adjusted intakes. Old rats drank only half as much water as young rats in response to sc hypertonic NaCl when intakes were adjusted for bw. Old rats drank less 0.3 M NaCl than young rats following overnight food and fluid restriction when intakes were adjusted for bw. In response to captopril adulteration of the drinking water, young rats significantly increased daily ingestion of 0.3 M NaCl when it was available in choice with water, and significantly increased daily water intakes when water was solely available, both in terms of absolute intakes and bw-adjusted intakes. Old rats had no response to captopril treatment. These results add important new information to previous reports that aging rats have diminished thirst and near-absent salt appetite responses to regulatory challenges.