The present study evaluated the differences in aerodynamic behavior between the 1990 Provox and 1986 Staffieri voice prostheses for total laryngectomy patients. Both prostheses were submitted to in vitro laboratory testing to assess their aerodynamic behavior under different conditions of air flow through the valve and tracheal side pressure. In addition, six patients using the Provox and another six using the Staffieri prostheses were submitted to a dynamic study of phonation. This latter study evaluated the intratracheal pressure corresponding to the different intensities at which the vowel sound /a/ was pronounced. In vitro measurements revealed significant differences between the two prostheses, with the best results achieved with Provox. In contrast, the in vivo measurements did not reveal any significant differences between the two groups of patients in the 50-79 dBSPL range, although there was some difference at intensities equal to or greater than 80 dBSPL. Again, in this latter case the best results were achieved with the Provox. However, the ideal prosthesis has yet to be found. In some patients, the so-called low-resistance prostheses fail to maintain their aerodynamic performances, most likely because anatomic resistors interfere with the effort (i.e., pressure) required to produce a voice. At present the choice of prosthesis is best determined on an individual patient-to-patient basis.