Cigarette smoke (CS) is a leading known cause of cancer and cardiovascular diseases worldwide. The mechanisms by which CS produces its damaging effects seem to be multifactorial. Among others, CS toxicity is due also to several compounds like alpha,beta-unsaturated aldehydes (acrolein, crotonaldehyde) and saturated aldehydes (acetaldehyde). Aldehydes could interact with thiol compounds of salivary proteins, leading to structural and functional alterations of these molecules. Prior in vitro studies have shown that there is a significant decrease in several known enzymatic activities following exposure to CS. Additionally, it was found that glutathione (GSH) has protective effect against the damaging role of CS to salivary enzymes, emphasizing the role of thiol groups in the mechanism of inactivation of these enzymes. In this study, salivary amylase activity showed a significant inhibition following exposure to CS, and to external addition of purified aldehydes known to be present in CS, due probably to the interaction between aldehydes and -SH groups of the enzyme. Our results indicate that although saturated aldehydes are the chief aldehydes present in CS, a significant decrease in amylase activity was due to unsaturated aldehydes, reacting, probably, through their double bond with the thiol group of proteins by the Michael addition reaction.