Changes in oxidation of lipides and working out a new method of llberating malonic dialdehyde by means of alkaline hydrolysis and with thiobarbituric reaction as a measure of utility value of raw materials, food pro-ducts, feeding atuffs and ttechnical products. There habe been analysed chemical changes and physico-chemical properties of lipides as regards their suscep-tibility to oxidation and oxidizing polymerization. There have been investigated properties of lipides, taking into consideration limited possibilities of the hither ways and methods of izolating low-molecular compounds characterizing guality of products. The attention has been drawn mainly to a possibility of 1iberating malonic disldehyde, as an indicator substance, from primary and secondary compounds. There have been investigated and selected the optimum parameters of determining a degree of oridation of lipides in raw materials, food products, feeding stuffs and natural products assigned to technical purposes by means of a thiobarbituric method used together with alkaline hydrolysis. On the grounds of investigating 58 raw materials and products, it has been assumed that the most favourable conditions for the thiobarbituric method with alkaline hydrolysis are the following: a 5 minute hydrolysis for fatty and fatty protein parent substances, and a 15 minute hydrolysis for the parent substances of predominance of carbohydrates compounds in the agueous solution 0,35 N of soda alkalies, acidifloation of the hydrolyzed test specimen to pH 0,5 by means of the HCl solution containing 5-8 g NaCl analar, tha marimum distilling off malonic dialdehyde together with steam and causing the acidified to pH 1,5 distillate in the presence of a reagent of 2-thiobarbituric acid for 25 minutes.