The measurement of mouth pressure during a maximal inspiratory effort against a quasi occlusion (maximal inspiratory pressure (MIP)) is classically established as the standard for assessment of inspiratory muscle strength [1]. However, in addition to being closely dependent on subject collaboration, this manoeuvre is demanding and unpleasant. Thus, whilst high values of MIP exclude inspiratory muscle weakness, lower values are frequently difficult to interpret, reflecting either a true muscle weakness or a lack of motivation and co-ordination [2].A recent alternative noninvasive method consists of performing a short maximal sniff through one nostril while measuring nasal pressure through a plug occluding the contralateral nostril (sniff nasal inspiratory pressure (SNIP)) [3][4][5]. This natural manoeuvre is easier and less unpleasant than the static effort of MIP, but nevertheless depends on volitional muscle contraction. The need for a nonvolitional test, especially in situations where collaboration is totally lacking, has led to the development of phrenic nerve stimulation. Because it is better tolerated and easier to apply, cervical magnetic stimulation has now largely replaced electrical stimulation [6,7]. The measurement of twitch mouth pressure (Pmo,tw) during magnetic stimulation was recently reported as a reliable assessment of diaphragm strength [8].Thus, several noninvasive techniques are now available for assessing inspiratory muscle strength, based on volitional and nonvolitional manoeuvres. In order to use these new methods in clinical settings, it is necessary to characterize them in comparison with the established reference method. The aim of this study was to determine the reproducibility of SNIP and Pmo,tw during cervical magnetic stimulation and to compare them to classical MIP in a group of normal subjects. Materials and methods Study subjectsTen healthy volunteers (nine males, one female) were studied. Their characteristics were (mean±SD): age 28±7 Ten healthy subjects were studied at functional residual capacity in semirecumbent position. Cervical magnetic phrenic nerve stimulation was performed during gentle expiration against an occlusion incorporating a small leak. Constancy of stimulation was controlled by recording diaphragmatic electromyogram. Within and betweensession reproducibility of pressure were studied for Pmo,tw, SNIP, and MIP. The subjects were studied during a session of 10 manoeuvres repeated after 1 day and 1 month.The mean values were 16 cmH 2 O for Pmo,tw, 118 cmH 2 O for SNIP, and 115 cmH 2 O for MIP. For the three tests, the within subject variation was small in relation to between-subject variation, with the intraclass correlation coefficient ranging 0. We conclude that the within session reproducibility of the new tests twitch mouth pressure and sniff nasal inspiratory pressure is sufficient to be clinically useful. For sniff nasal inspiratory pressure, the between session reproducibility established after 1 day was maintained after 1 month. For twitch mouth pressure,...