We measured the maximal inspiratory and expiratory pressures of 200 healthy subjects (94 men and 106 women) using a membrane manometer designed by the authors. The reference intervals for maximal inspiratory pressure in men were -5 to -15 kPa, and for maximal expiratory pressure 9–21 kPa. For women the reference intervals for maximal inspiratory pressure were -3 to -14 kPa and for maximal expiratory pressure 5–15 kPa. In clinical practice only the lower limits are significant. The differences between subjects of different ages were small, thus age has little bearing on the strength of respiratory muscles in healthy men and wo