Since the seventies the « mystery of Bulgarian voices » is famous all over the world. We try to discover it by studying forms of vocal polyphony observed in west-central and south-west Bulgaria, in the areas of Pazardzhik and Ihitman, Velingrad and west of the Stara Planina. Polyphony with a drone predominates : a note held by a group supports the skillful melodic performance of the soloist. But the second voice may be very variable (in the interior of the country), the drone may be sung by two, three or four voices (like in peripheral areas) and give rise to erudite forms of heterophony. We thus note how Bulgarian polyphony conveys mythological symbols, both in the terms used to characterize it and in the virtuoso practice of the melodic ornamentation. We start from the hypothesis that mythological symbols are preserved not only in the form, but also in the body language used in rituals in which these musical forms are expressed.