This paper will review recent findings coming from a research program in which the acoustic properties of various types of alaryngeal speech were examined. The fundamental frequency, rate, phonation time, long-term spectral, and vowel-formant frequency characteristics of male and female esophageal talkers were measured in an attempt to provide information about the physical properties of esophageal speech and to find correlates to listeners' judgments of the sex of these speakers' voices. Significant sex differences were found for some of the physical measures. These studies show that close relationships can be found between the acoustical and perceptual spaces of esophageal voices. In other experiments, the acoustical properties of two other types of alaryngeal speech—buccal and pharyngeal speech—were measured in an attempt to evaluate their potential use as primary methods of alaryngeal speech. Studies of the mechanism of phonation, fundamental frequency, phonation time, rate, intelligibility, and long-time spectral characteristics of buccal and pharyngeal speech were completed. The results of these experiments support the hypothesis that both buccal and pharyngeal speech do not represent efficient or practical primary methods of alaryngeal speech.