Pinoresinol dimethyl ether, secoisolariciresinol, lariciresinol, isolariciresinol and isolariciresinol-4' methyl ether were isolated from the knots of dead trees of Araucaria angustifolia. The 13C NMR spectra of these compounds, their methyl and acetyl derivatives, and the corresponding one of matairesinol, have been recorded and the signals assigned. On the basis of these assignments, the structure of the new monomethyl ether of isolariciresinol has been established.