AbstractFatty acid composition of wheat flour oils was measured by gas chromatography, and results were presented either as fractions of the total C16 and C18 acids or, by application of an internal standard, as the percentage of each acid in the original oils.Flour treated with chlorine dioxide (up to 120 p.p.m.) and stored for periods up to 15 weeks showed no changes in the fatty acid composition of the mixed oil extracted successively by light petroleum and acetone. Heavier treatment resulted in significant oxidative changes. After 27 weeks' storage, however, both untreated and lightly treated flour (up to 33 p.p.m. of ClO2) showed changes in the acetone—but not in the light petroleum—extracts. These findings were correlated with measurements of the induction periods of whole flours when heated in oxygen at 100°, both treatment and storage diminishing the induction periods.Chlorine treatment of the flour caused decreases in linoleic acid contents of the extracted mixed oils at all levels of treatment. The effect on induction period was complex, but in general chlorine treatment caused long induction periods, which diminished during storage less than those of untreated flour. The significance of these results is discussed.