In order to immunolabel heartwood extractives in Japanese cedar (Sugi, Cryptomeria japonica), we attempted to prepare antibodies against agatharesinol, a major norlignan of these heartwood extractives. Agatharesinol by itself is not antigenic due to its low-M(r), and thus was covalently bound to bovine serum albumin in order to synthesize an antigenic hapten-carrier conjugate (artificial antigen). The number of agatharesinol molecules per artificial antigen molecule was estimated as 27-28 by quantifying Lys in an acid hydrolysate of the artificial antigen by HPLC. Reaction between the artificial antigen and serum obtained from a rabbit immunized with the artificial antigen was competitively inhibited by agatharesinol, indicating the successful production of anti-agatharesinol antibodies. Inhibition by sequirin C, another major norlignan in Sugi, was weaker than that by agatharesinol. Furthermore, an EtOAc soluble fraction, which contains mainly norlignans, inhibited the reaction more strongly than any of the other fractions of Sugi heartwood extractives. Thus, the antiserum we have produced reacts most strongly with agatharesinol and recognizes norlignans almost selectively among Sugi heartwood extractives.