The research proposed herein provides an interdisciplinary approach toward the elaboration of environmental conditions that will adequately satisfy the physiological requirements for laboratory animals and simultaneously minimize expensive control systems for animal rooms. Utilizing a calibrated environmental chamber, heat dissipation of dogs was measured by direct calorimetry to determine the influence of varying the temperature, humidity and air changes of the animal spaces on the Standard Heat Ratio (SHR) and Sensible Heat Ratio (R) of the animals. Isostate conditions (ventilation performance) will be determined as a function of air change rate, configuration type and density of cages and rate of contamination production. As significant differences between cage and environmental chamber indicate that ventilation rates within a microenvironment may differ from the ambient condition, an evaluation will be made of design improvements and/or alternate cage design criteria. BIBLIOGRAPHIC REFERENCES: Chen, C. L. and E. L. Besch. Effect of altered photoperiod on estrous cycle, pregnancy and onset of puberty in the rat. Biol. Reproduction. 12:396-399, 1975. Besch, E. L. Animal cage-room dry-bulb and dew-point temperature differentials. ASHRAE TRANSACTIONS. Vol. 81 (Part II), 1975.