From the epigeal part of Nitraria sibirica has been isolated a new alkaloid with mp 184-185°C (methanol), [α]D ± 0°, which has been called nitrabirine. On the basis of chemical transformations and an analysis of the spectral characteristics (mass, IR, UV,1H and13C NMR spectra), its structure has been established as spiro{cyclohexane-1,3′-(3′,4′,5′,6′-tetrahydropyrido [1′,2′:1″,2″]imidazole)}-2-ol, and a conformation has been suggested. © 1983 Plenum Publishing Corporation.