It has been found that malondialdehyde penetrates during smoking through filters and exhales with smoke from cigarettes such as: "Pall Mall", "Winston", "Camel", "Lucky Strike", "Kansas", "Mustang", "Ronson", "Chesterfield", "Rally", "Oscar" and "Marlboro". These cigarettes exhale malondialdehyde in a different way, in free form in the amount from 8.5 to 23.5 mg/kg cigarettes on an average of 13.3 mg/kg for the whole group and totally (in free and bounded form) from 9.5 to 26.5 mg/kg (average 16.9 mg/kg). Moreover, it has been found that filters retain this aldehyde in free form on an average of 9.9 mg/kg and totally (in free and bounded form) of 19.0 mg/kg. Without filters these amounts would increase aldehyde contents in smoke by 42.7 and 52.9%, respectively. Low malonalogenic properties of tobacco, high effectiveness of cigarette filters, high degree of tar deposition before inhaling into lungs and slow (6 min and longer) smoking decide about low level of exhalation of malondialdehyde in cigarette smoke.