To date, only one study has empirically examined the effects of sitting versus standing posture on the spirometric forced expiratory volumes. Because of design limitations, the small excess of sitting over standing values found in that study may have been due to a positive testing order effect. Using a crossover design, the present study of 90 middle-aged male subjects alternated the sitting-standing and standing-sitting testing sequence between subjects to avoid confounding by testing order effects. The major findings were that forced expiratory volumes in one and in six seconds and forced vital capacity were significantly larger (p less than 0.001) in the standing than in the sitting posture, with mean standing minus sitting differences ranging from +0.06 to +0.08 L for the 3 indexes. The larger expired volumes measured in the standing position in this study were probably due to the subjects taking slightly larger inspirations in this posture than in the sitting position.