Residues of inorganic insecticides used on tobacco have decreased to the extent that they are primarily of academic interest only. Organic pesticides used for control of pests, including sucker growth, can often be detected at high levels during the early phases in the culture of tobacco due to the large surface-to-weight ratio characteristic of leafy products. Residues of 100 ppm are not uncommon for stable pesticides on green tobacco ready for harvest and even pesticides which normally dissipate quickly after treatment, as parathion, may exceed 4 ppm following normal treatment. During the flue-curing process, from 40-99 per cent of the residues disappear. Air-curing is much less effective in destroying the residues as would be expected. During smoking of cigarettes 80-90 per cent of such stable compounds as the chlorinated hydrocarbons is decomposed or transferred to the sidestream smoke whereas less stable pesticides, as phosphate insecticides or carbamate fungicides, are normally detected in mainstream smoke at levels less than 5 per cent of that present in the cigarette before smoking. The fate of TDE, the most common insecticide found in mainstream cigarette smoke from commercial cigarettes, appears to follow the same route of degradation in mammalian systems whether inhaled or introduced orally. The levels of pesticides found in mainstream smoke of commercial cigarettes, or expected from recommended treatment, are below the tolerance ascribed on food by several countries. However, additional research is needed to clarify the contribution of applied pesticides from the same compounds produced pyrolytically during cigarette consumption. Continuous surveillance of manufactured tobacco for pesticide residues, increased research on the isolation and identity of decomposition products in mainstream smoke, and augmentation with non-pesticidal or decreased pesticidal methods should be encouraged.