Conducted 2 experiments in which 28 male hooded Listar strain rats maintained on food-deprivation schedules received 2-ml intraperitoneal injections of hypertonic (6%) or isotonic (.9%) NaCl. Hypertonic injections produced inhibition of eating. Allowing Ss to drink water ad lib completely canceled the inhibition, but for Ss without water each milliliter of water deficit produced had the effect of subtracting approximately 1/3 gm. of food from the amount eaten. The size of this effect was entirely independent of the level of food deprivation. Allowing an inhibited S to drink measured quantities of water produced disinhibition at the same rate (i.e., approximately .33 gm. of food/1 ml. of water). Changes in body fluid composition induced by food eaten also inhibited intake in exactly the same fashion. Results indicate that states of the body fluids that produce thirst inhibit feeding, and for lower levels of hypertonicity this inhibition is approximately constantly proportional to the water deficit. A direct subtractive neural inhibition arising from the system controlling drinking upon the system controlling eating adequately explains these results. (18 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)