Dietary administration of the angiotensin converting enzyme inhibitor, captopril (0.70 g/kg of food), to female rats for 1 week was accompanied by a spontaneous appetite for 0.25, 0.30 or 0.35 M NaCl solution when choice was offered between any one of them and distilled water to drink. An additional experiment was performed to determine the NaCl preference threshold concentration for each group. Control and treated rats were offered choice between two drinking bottles containing distilled water and a NaCl solution, respectively. The concentration of the latter varied from 0.0006 to 0.350 M/l. Control rats could detect the difference between water and NaCl solution at a concentration of 0.030 M/l, whereas captopril-treated rats detected the difference at the lowest concentration offered, i.e., 0.0006 M/l. Captopril-treated rats also preferred 5% glucose solution to distilled water, as did untreated controls. Similar results were observed for 0.25% saccharin. No difference between groups was observed when choice was offered between distilled water and dilute solutions of HCl. Thus, a NaCl appetite developed within 1 week of treatment with captopril. The appetite was accompanied by an ability to detect NaCl at a 50-fold lower concentration than that of the control group. Administration of captopril was also accompanied by an appetite for glucose and saccharin but not for HCl.