Since the early 70's many experimental studies have pointed out the existence of a close relationship between the acoustic characteristics of voice and the physical features of the speaker. The purpose of this study is to determine, on one hand, whether listeners are capable of identifying age, weight and height of speakers; on the other hand, to verify on the basis of perceptive tests, whether it is possible to distinguish twin's voices with better than chance-guessing accuracy. The results give rise to various considerations. Suggestions for future research are discussed.