Abstract A procedure was developed for the determination of the composition of important“off-flavour alkanals” formed in the autoxidation of fats. The volatile carbonyls were isolated from the fat (5–10 g) by steam distillation by using an inert stripping gas and then trapped as their 2,4-dinitrophenylhydrazones on a solid support. Qualitative and quantitative evaluations of the alkanals were carried out by gas chromatography via the adsorbed 2,4-dinitrophenylhydrazones. The proposed procedure was tested on chicken fat autoxidized to various extents. In this study, a close correlation was obtained between the peroxide value (16–118) and the n-hexanal content (0.05–1.9 μg per gram of fat).