The action of drugs on circular smooth muscle from rabbit renal artery, renal vein, mesenteric vein, inferior vena cava, guinea pig bronchus, and mouse trachea was studied using an inexpensive modification of the method of Bevan, Nielsen and Ovvman, and Bevan and Osher. Two 30-gauge disposable stainless steel hypodermic needles supported the tissue rings in a standard 10-ml isolated muscle bath. All the blood vessels contracted to norepinephrine, histamine, and KCl. The veins, unlike the renal artery, did not respond maximally to KCl and did not contract at all to serotonin. The guinea pig bronchi contracted to carbachol, histamine, and KCl and relaxed to isoproterenol. The mouse trachea contracted maximally to carbachol, did not contract to histamine, and contracted to 50% of maximum in response to KCl. Thus, standard isolated tissue baths can be inexpensively adapted for the study of relatively small blood vessels and airways (about 1 mm in diameter).