1. The relation between urine and rectal temperatures has been studied under a variety of conditions by using the Uritemp bottle, which measures deep body temperature from the urine. 2. This device gives a reliable measurement of deep body temperature and has advantages over both rectal and oral techniques for many clinical applications. 3. The development of a new and more reliable device, the Uritemp meter, is described. Urine is voided through a specially designed and disposable unit, equipped with either a standard mercury-in-glass thermometer or any one of a range of commercially available electronic thermometers. Provision is made to collect a urine sample simultaneously if required.