Continuing an investigation of the alkaloids of the epigeal part of Nitraria schoberi L. [1], we have isolated a new alkaloid schoberidine (I) with the composition C20H21N3 and molecular weight 303 (mass spectrometrically). Schoberine, a yellow substance with mp 204-205°C, has a yellow-green fluorescence in solution and forms a salt with ethanolic HCl (mp 267°C, ethanol). Comparison of the compositions of schoberidine and nitrarine indicates that (I) is a tetradehydro derivative of the latter. The mass spectrum of (I) shows ions at m/e: 303 (M+), 275, 274, 260, 259, 220, 219 (100%), 195, 182, 169, 168, 83; the ion at m/e 275 (M-28) is formed by ejection of a dimethylene group from the molecular ion, and the intense ion at m/e 219 (tetramethylene-β-carboline fragment from ejection of a piperidine ring) suggests a factor (likely a double bond at the third position of the nitrarine molecule) stimulating its formation, with the mass difference from nitrarine's analogous ion (223) indicating double bonds in the β-carboline part. The UV spectrum of schoberidine salt changes with pH: in ethanol, maxima are 254, 308, 372 nm (β-carbolinium ion absorption, slight bathochromic shift with acid); in alkali, maxima are 284, 330, 415 nm (considerable bathochromic shift), behavior typical of anhydronium bases (similar to melionine E and F [2]). Consequently, schoberine is an anhydronium base.