The inner and outer barks of ponderosa pine (P. ponderosa) have been pyrolysed at 350°C in vacuum and the tars analyzed by gas chromatography after tri-O-methylsilylation. The nine major peaks in the gas chromatogram have been identified and quantified and it is concluded that all (except pinitol) originate predominantly from polysaccharide components of the barks. They account for up to 53% of the total tar. Removal of most of the metal ions from the barks by ion exchange with dilute acid has a dramatic influence on the tar constituents, e.g. increasing the yield of levoglucanosan from inner bark from 0.8% to 13%. which represents 31% of the original glucan content of the bark. The polyphenol and lignin components of the bark are predominantly converted directly to char at 350°C.