A fractionation and analytical procedure is described for the measurement of the unavailable carbohydrates in foods. The scheme provides values for water-soluble polysaccharides, hemicellulose, cellulose and lignin. Tests used to investigate the reliability of the methods are reported and the results obtained with a range of foodstuffs are presented. From the results obtained it is possible to derive values for the composition of the cell-wall material of these foods. The results are in agreement with more detailed studies of the composition of the cell walls of plants.