In 32 patients with proven diagnosis of muscular subaortic stenosis, auscultation and phonocardiography were performed in the following positions: supine, supine with the legs passively elevated, standing and squatting. The same studies were carried out during the Valsalva maneuver and before and after the administration of phentolamine and the inhalation of amyl nitrite. Passive elevation of the legs resulted in attenuation of the systolic murmur in 73 % of the patients while the standing position increased it in 52% of the cases. Squatting softened the systolic murmur in 87% of the patients and the Valsalva maneuver induced an opposite effect in 58% of them. Amyl nitrite and phentolamine accentuated the systolic murmur markedly in all patients. Similar responses in direction and magnitude were not observed in patients with other cardiac diseases or innocent systolic murmurs.