Lignin model compunds l-(3,4-dimethoxyphenyl)-2-(2-methoxy-phenoxy)-propane-1,3-diol (veratrylglycerol-0-guaiacyl ether) and l-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-propane-1.3-diol (guaiacylglycerold-guaiacyl ether) were completely consumed after reaction with 85% formic acid for 1 hour at reflux temperature. In both cases less than 25% @-ether cleavage (monitored by guaiacol formation) was observed. During the early stages of the reaction, the primary, secondary and phenolic hydroxyl groups were partially converted to the corresponding formate esters. The intramolecular condensation products 2,3-dihydro-3-(3,4-dimethoxyphenyl)-7methoxy-2-benzofuranmethanol and 2,3-dihydro-3-(4-hydroxy-3-methoxyphenyl)-7-methoxy-2-henzofuranmethanol were isolated as their corresponding formate esters and were the major products observed from the reactions of the etherified phenolic and the free-phenolic model compounds respectively. Yields of monomeric acidolysis products were low, and the overall mass balance for the system indicated that about 50% of the reaction products were not detected under the gas chromatography conditions used. 'H NMR spectra showed the presence of high molecular mass species at longer reaction times.