1. Studies on rape-seed oil have shown that the determination of oxypolymers by means of the method according to Rost (determination of fatty acids insoluble in petroleum ether) yields unsatisfactory results. By way of contrast, the gravimetric determination (after isolation of the polymers via the non-urea adduct fatty acid methyl esters and thin-layer chromatographic separation), as proposed by the authors, permits to obtain results of good reproducibility and to determine thermopolymers and oxypolymers separately. 2. During the refining of rape-seed oil, it was observed that its polymer content decreased considerably on bleaching, and increased on deodorizing.