Investigations and literature concerning the use of hallucinogens among indigenous groups in the Amazon basin have been increasing at a rapid rate. One aspect of the use of hallucinogens that needs further investigation is the role of cultura:l variables in the altered states of consciousness induced by drugs. Although Wallace (1959) drew attention to the problem some years ago, only a few studies have addressed themselves directly to it. The purpose of this paper is to present a brief description of the use of yage (Banisteriopsis) among the Siona Indians of the northwest Amazon basin with reference to the cultural influences on the yage experience. Two Siona texts will be presented to illustrate the nature of "culturally influenced" visions.