BACKGROUND: Minor differences in technique may account for the wide range of published normal values of maximum expiratory and inspiratory pressures. The effects of holding the lips while the subject performed a maximal expiratory pressure manoeuvre were investigated in this study. METHODS: Maximum static expiratory pressures (PEmax) obtained with a cylindrical tube by means of lip compression by the subject and technician aided compression were compared in 20 men (mean age 27 years) and 20 women (mean age 28 years). RESULTS: Technician aided lip compression was associated with higher maximum expiratory pressure than compression by the subject in both men (195 v 110 cm H2O) and women (134 v 80 cm H2O). CONCLUSION: Compression of the lips and corners of the mouth should be performed by a trained technician for maximum expiratory pressure measurements when a cylindrical mouthpiece is used.