Performance of four Spirostat units in measuring forced expiratory volume, 1 sec (FEV1) and forced vital capacity (FVC) were examined against that of a Collins spirometer using 10 volunteers. One Spirostat was discarded because of gross inaccuracy. The other three were evaluated for accuracy, repeatability and comparability among Spirostats. For FEV1 it reads high over the low ranges and low over the upper ranges. For the FVC, it reads high for all values up to 5.0 liters where it becomes quite accurate. The repeatability was considered only fair, since one spirostat differed from the other two; the comparability was acceptable.