AbstractCell walls of plant parts of maize, barley, Italian ryegrass, wheat bran, lucerne and red clover were subjected to low voltage pyrolysis‐mass spectrometry. The ion intensity at m/z 120, which is characteristic ofp‐coumaric acid, was significantly correlated (r=0.99) with thep‐coumaric acid content of the walls; the ion intensity at m/z 150, characteristic of ferulic acid, was present in the spectra of the graminaceous walls. Factor analysis of the pyrolysis‐mass spectra indicated that some, at least, of thep‐coumaric and ferulic acid constituents of the walls are bound to pentosans, and suggested that not all the aromatic constituents of the walls are bound to polysa