In the cultured cells of Corydalis incisa, (-)-enantiomers of the α-N-metho salts of the trans- and cis- 13-methylprotoberberines having trans and cis configurations of the protons at C-13 and C-14, respectively, were stereospecifically bioconverted into the (-)- and (+)- 13-methylprotopines [( -)-( 13s)- and ( +)-( 13R)-enantiomers], respectively. The α-N-metho salts of the eight different 13-methylprotoberberines were demonstrated to be the precursors of the 13-methylprotopines, though there is a difference in conversion yields. The α-N-metho salts of the trans- 13-methylprotoberberines bearing a methylenedioxy bridge at C-2 and C-3 are more favorable precursors of the 13-methylprotopines than those having methoxyl groups at the same positions. The α-N-metho salts of cis-13-methylprotoberberines with either methylenedioxy or methoxy substitution are efficiently converted into 13-methylprotopines. The ( + )-( 13R)- 13-methylprotopines were more effective precursors of the benzophenanthridines than the (-)-(13S)-methylprotopines. The 13-methylprotopines possessing a methylenedioxy bridge were more preferred precursors of the benzophenanthridines than those having methoxyl groups. (+)-Corynoline [14] is more easily oxidized than (-)-14, resulting in (+)-corynoloxine [18]. (-)-Corynoline is acetylated more easily than its (+) isomer to afford (-)-acetylcorynoline [19]. Corynoline analogue 15, having methoxy groups at C-7 and C-8, must not be as easily oxidized as corynoline, which has a methylenedioxy bridge at C-7 and C-8. (+)-Chelidonine [27] was converted into dihydrosanguinarine [32] and dehydrochelidonine [28]. Biotransformation of the protoberberines into the benzophenanthridines occurred similarly in both cultured cells and live whole plants of Co. incisa. Two different biogenetic pathways (Scheme 1) from the protoberberines have been defined in several Corydulis species (Corydulis incisa, Corydulis ophiocarpa, Corydulis ochotensis var. raddeana, Corydulis platycarpa, and Corydulis pallida var. tenuis), Macleaya cordata, and Chelidonium majus of Papaveraceae using whole plants or their cell cultures (1-6). The first pathway involves the sequence protoberberine or 13 methylprotoberberine→α-N-metho salt→protopine→benzophenanthridine; while the second includes the conversion 13-hydroxyprotoberberine→α-N-metho salt→13 oxoprotopine→spirobenzylisoquinoline or benzindanoazepine (Scheme 1). The purpose of this work was to investigate the stereospecificity of the first pathway and to compare the biotransformation of the alkaloids in the cultured cells with that in Co. incisa plants. Some related experiments with the cultured cells of Co. ochotensis var. raddeana and Co. ophiocarpa were also covered.