Braintree Scientific's ECU is a new concept in small rodent experimental research. The ECU provides comfortable containment of experimental animals to facilitate repeated measurements of physiological and pharmacological parameters. Not a restrainer: animals are preconditioned (trained) to accept appropriate periods of confinement in the ECU. Blood pressure, clearance, and metabolism studies are better and easier using ECUs. The Braintree Scientific ECU consists of a molded plexiglass canopy hinged to a plexiglass base. Canopy has a tapered opaque plastic hood to protect the animal from visual disturbances. Multiple slots and an end plate allow adjustment of the canopy length for animal size and easy access to dorsal catheters and electrical leads. The base has a large through drilled slot for accessing ventral catheters, feces and urine. Four comfortable slots are provided to support the feet. The Braintree Scientific ECU is set up in position with the required equipment. The animal is placed in the ECU and the catheters and leads connected to the appropriate devices. Our ECU has been used for studies of anti-hypertensive drugs: development of hypertension as a function of age, renal and drug c clearance, metabolism, and endocrinological studies. ECU units are tailored for different sizes of rats and mice as a function of body weight. For best results, animals should be conditioned to appropriate periods of confinement in the ECU. This is easily achieved by introducing animals to the ECU daily for increasing periods of time.