Feeding of chemically synthesized [27-13C]codisterol ([27-13C]2), [27-13C]24-epicodisterol ([27-13C]3), [23,24-2H2]codisterol ([23,24-2H2]2), and [26,27-2H6]24-methyldesmosterol ([26,27-2H6]8) to Oryza sativa cell cultures, followed by MS and NMR analysis of the biosynthesized dihydrobrassicasterol (9)/campesterol (10), revealed that both (24R)- and (24S)-epimers of 24-methyl-Delta25-cholesterol (2/3) were converted to 9 and 10 via the common intermediate 24-methyldesmosterol (8).