The proof of the structures of two isomeric alkaloids — nitramine and isonitramine — from two species of plants of the genus Nitraria is given. Their diastereoisomerism with respect to the C7 asymmetric atom has been established. This is the first time that alkaloids with the structure of 2-azaspiro[5,5]undecan-7-ol have been found. © 1982, Plenum Publishing Corporation. All rights reserved.