Mahonia nepalensis DC. (also called Berberis nepalensis Spreng.) contains about 0.43% of umbellatine, C₂₁H₂₁O₈N, the alkaloid present in the Himalayan species of Berberis, B. umbellata Wall. and B. insignis Hook. f., and 0.02% of a hitherto unknown red alkaloid, neprotine, to which a provisional formula, C₁₉H₂₁O₆N, is given. Some of the physical properties and the hydrochloride and chloroplatinate of neprotine have been described. The seasonal variation of the total alkaloidal contents of different parts, roots, stem-barks and stems, of the plant as well as those of individual alkaloids, umbellatine and neprotine, are recorded. It is found that the highest concentration of alkaloids, e. g., umbellatine, 0.48% and neprotine, 0.02%, is in the roots of the old plants, during the winter months.