In order to distinguish between ortho-para and para-para phenol coupling in colchicine biosynthesis, [3'-(OCH3)-C-14]autumnaline was converted to [C-14]colchicine in seeds of Colchicum autumnale and the product was then selectively demethylated by a bacterium that exclusively demethylates C-3 of colchicine. The retention of the radioactive label in 3-demethylcolchicine indicates that biosynthesis proceeds through para-para coupling. (C) 1997 Elsevier Science Ltd.