Digital computers are often used in work physiology to find pulmonary gas transfer on a breath-by-breath basis. A measurement procedure was simulated to determine the effects of sample rate, signal noise levels, and numerical filters on the digital calculations. The results indicated that a trapezoidal rule integration at a sample rate of 30 hz with no numerical filter can provide satisfactory data. The flow rate and concentration signals should not be out of phase by more than 25 msec. The simple computational procedures give accurate results while minimizing the memory requirements and computation time.