This paper describes a unique singing mode, tentatively labeled “polyphonic overtone singing”. In overtone singingthe vocal harmonics of a stabile fundamental frequency are filtered by the singer in such a way that specific upper harmonics are amplified, and heard clearly, as a second musical voice. In the “throat singing” of Tuva (Mongolia) moving overtones usually occur over astable drone. In polyphonic overtone singing not only the pitch of the overtonesare changed and moving, but also the fundamental which results in two-voice singing.