SummaryOrgan‐mineral particle‐size fractions, isolated from five soils by ultrasonic dispersion in water, were extracted with anhydrous formic acid/acetylacetone before and after treatment with aqueous HF partially to destroy silicate material. The resulting residues from two of the clay fractions, one montmorillonitic the other kaolinitic, were extracted further using the same reagents and also with 0.5M NaOH. The pattern of nitrogen extraction and nitrogen distribution data for the size fractions of four soils was similar but those of a fifth soil, with a high content of amorphous oxides, were quite different. There was evidence that the increasing nitrogen contents of successive samples of extracted material were mainly due to an increased amino acid content, especially dibasic acids. A serial extraction of clay fractions using formic acid/acetylacetone followed by HF followed by formic acid/acetylacetone and finally NaOH dissolved approximately 90 per cent of the organi