The biosynthetic pathway leading to the dihydrobenzofuran neolignan (+)-conocarpan in Piper regnellii leaves, was demonstrated by means of in vivo administration of labeled l-phenylalanine [U-14C] and by enantioselective conversion of p-hydroxypropenylbenzene to (+)-conocarpan (85% ee) by an enzyme fraction obtained from its leaves. The enzyme preparation was devoid of general peroxidase activity and showed substrate specificity towards p-hydroxypropenylbenzene since p-coumaric acid, p-coumaryl alcohol and E-isoeugenol were not converted to any product naturally occurring in the intact plant.