Since its introduction, the Sundberg model of the laryngeal system as the resonance source of the singer's formant has gained wide acceptance. However, no studies directly testing this hypothesis in vivo have previously been reported. Thus, the present study was undertaken to test this hypothesis on three classically trained professional male singers. The vocal behaviors of the singer-subjects were evaluated during model and pulse register phonation via magnetic resonance imaging, strobolaryngoscopy, and acoustic analysis. Results indicated the subjects did not achieve the laryngopharyngeal/laryngeal outlet cross-sectional area ratio requisite to the model and that the formant remained robust in pulse register phonation. It was concluded that these subjects' behaviors were not consistent with Sundberg's model and that the model was inadequate to account for the generation of the singer's formant in these three subjects.