The role of the subfornical organ (SFO) in drinking caused by cellular dehydration and angiotensin was examined in the dog. Drinking responses to intravenous administration of angiotensin and to hypertonic NaCl were compared before and after electrolytic ablation of the SFO. After destruction of the SFO, drinking in response to angiotensin was 0.5 ± 0.3 ml/kg compared to 11.9 ± 3.7 ml/kg prior to lesioning. Drinking in response to hypertonic NaCl was not affected by lesioning the SFO (12.6 ± 6.6 ml/kg before vs. 13.4 ± 5.4 ml/kg after the lesion). Lesions superior or lateral to the SFO did not affect drinking in response to either angiotensin or hypertonic NaCl. These data show that the SFO is essential for drinking in response to blood-borne angiotensin but not to the stimulus of cellular dehydration in the dog.