The major alkaloids present in very young leaves of Mitragyna speciosa from Malaysia were shown to be highly conjugated indoles, mitragynaline and corynantheidaline. Related compounds are also present in smaller amounts and two others were isolated and characterized (named mitragynalinic acid and corynantheidalinic acid). Mitragynaline is also present as a minor component in mature leaves of the plant. © 1990.