[en] The tobacco plant has been the object of extensive basic research about its genetic, culture, biochemistry and postharvest metabolism. In addition , much is known of its pyrolysis products and the conditions that affect the formation of these products. Tobacco smaoke is a concentrated aerosol of liquid particles suspended in an atmosphere consisting mainly of nitrogen, oxygen and CO2. While the precise chemical composition of the particular and gaseous phases is depended on the characteristics of commercial tobacco and the manner in which it is smoked, both phases contained tens of hundreds of individual constituents. Notable among potentially hazardous constituents of smoke are tar (mainly benzopyrene) nicotine, HCN, acrolein, N-nitrosamines, cadmium and polonium 210. recent advances in tobacco science make it possible to develop a safer tobacco that delivers undesirable smoke compounds at levels that are below the old values, but these results are biologically uninterpretable at present.