An apparatus is described with which the O2 consumption and C14O2 excretion of small laboratory animals can be recorded and integrated continuously during the course of experiments with C14-labeled compounds. In addition, the total CO2 production throughout intervals can be determined and the respiratory quotient calculated. The oxygen consumption apparatus is simple, inexpensive, and sensitive, and can be used in any closed metabolism system. apparatus; isotope; oxidative metabolism Submitted on July 10, 1964