The present article was given as a lecture at the XXII. Deutscher Orientalistentag in Tübingen (March, 1983) and deals with the problem of Soma. G. Wasson proposed a hallicunogenic mushroom, viz. the fly-agaric. It is shown that the severe criticism he met with on behalf of Indo-Iranian philology is justified in so far as it is impossible to classify Soma botanically, whereas it went too far in excluding the mushroom absolutly. Actually the solution cannot be found in the physical descriptions of the plant, but in the hitherto neglected type of the intoxication it produces. In this regard the information of the Vedic poets can be relied on. They furnish evidence of the alcaloidic nature of the active substance of Soma, because it produces especially optical and accustical delusions with changes in the dimensions of the objects perceived. This can be shown by a careful examination of many stanzas. These effects are the clue to most of the ‘mysterious’ Soma poems.