Pimax measurement is useful for quantifying the fatigue of the respiratory muscles (the "respiratory pump" of the mechanics of respiration), for controlling the therapeutic effect of artificial respiration performed at home, and assessment of the possibility of relieving a patient from artificial respiration. So far, such measurement had required complicated set-ups. A portable alternative is now available for Pimax measurement (MPM, distributed by Medanz, Starnberg, Germany). In a prospective study we compared the Pimax values measured via the mouth pressure measuring instrument under test, with the standard laboratory method. Statistical comparison of the measured data yielded a high degree of correlation (r = 0.97) with slight scatter of the individual data around the identity line. The portable instrument tested in this manner thus represents a mobile method yielding reliable Pimax values both on an inpatient and an outpatient basis.