The possibility of malonic dia1dehyde.formation in the tobacco smoke was investigated and the conditions of the degree of malonal generation by smoke compounds were stated. The malonal concentration in smoke of cigarettes with filters is in the mean lower (28.7 mg/kg) than in smoke of cigarettes without filters (35.0 mg/ kg). The highest contents of malonal were received in "Zefir" (41.7 mgjkg), "Radomskie" (35.2 mg/kg) cigarettes with filters and "Sport" without filters (42.6 mg/kg) and by a half lower in "Giewont" cigarettes with filters (17.8 mg/kg).The tobacco smoke is a mixture of many volatile compounds, which are formed as a result of tobacco pyrolysis in the presence of oxygen or by its limited access. The very active compounds undergo continuous interreactions. In the pyrolisate fractions of the tobacco smoke, the groups of inactive, basic, acid and phenolic, simple and complex substances have been distinguished [17]. GROWER et al.[lo] and SIMS [28] consider oxides and peroxides of aromatic hydrocarbons responsible for biological changes in living organisms. BOGDER [2] notices the possibility to form polycyclic compounds from simple dicarbonic compounds by condensation.In an other group of works it is said, that intra-and intermolecular transverse couplings in biogenic food components and in living organisms are caused by malonic dialdehyde (malonal), which is formed either from oxidized unsaturated fatty acids and hydrocarbons or from saccharides 121, 221. Malorial, as very reactive tricarbonic compound inactivates among others substances such as lysine, methionine, histidine, glutathione, heme proteins, structured proteins and enzymes, e. g. ribonuclease A, cytochrome C, succinate oxidase, glucose-6-phosphate dehydrogenase, /?-glucuronidase and DNA, RNA and also a number of other compounds 13-8, 12, 13, 15-18,201. The malonylation of amino acids, proteins and enzymes causes forming of protein-fatty complexes of specific physicochemical and pathological properties [21].