Continuing a study of the alkaloid composition of Thalictrum baicalense, the epigeal part of T. baicalense Turcz. collected on June 26, 1978, in the environs of the village of Ignashino, Skovorodino region, Amur province was investigated. 0.54% of total bases was obtained and separated into phenolic and nonphenolic fractions. From the nonphenolic fractions, a base (I) was isolated by chromatography on a column of alumina (eluent benzene) followed by preparative separation on plates with a fixed layer of silica gel in the benzene--ethyl acetate-methanol (20:20:3) system. Base (I) had mp 146--147°C (acetone), [α]D +55° (methanol). Its UV spectrum (ethanol: 217, 242, 291, 306, 318 nm max), NMR spectrum (CDCl3) showing signals from N-CH3, three methoxy groups, a methylenedioxy group at C-2-C-3, and characteristic protons at C-8 and C-II, as well as mass spectrum with M+ at m/z 369, indicated it was an aporphine alkaloid. The base was named baicalidine, identified as a new pentasubstituted base. Its structure was proposed as N-methyl-2,3 methylenedioxy-1,9,10-trimethoxyaporphine, confirmed by comparison with N-methylbaicaline obtained via Hess methylation of baicaline (II). Additionally, berberine, glaucine, and baicaline were isolated from the epigeal part of T. baicalense.