Using isolated, blood-perfused atrium preparation of the dogs, the effect of stretch on sinus rate was studied in 11 preparations. Stretching usually produced sinus acceleration in all 11 spontaneously beating atria. Within a range of 0--30 Gm, greater degrees of stretch produced greater degrees of sinus acceleration. During maintained stretch sinus rate slightly reduced but not to the control rate. On release from stretch sinus rate immediately returned to the control rate, and there was occasionally a slowing to rates lower than control in verapamil treated preparations. Atropine, adrenergic beta-receptor blocking agents, propranolol and carteolol, verapamil, and tetrodotoxin did not greatly modify responses to stretching.