The discharge flow mass spectrometric technique has been used to determine the absolute rate coefficients of the gas-phase reactions of Cl atoms with 3-pentanone (1) and 3-hexanone (2) in the temperature range 260333 K and at a total pressure of 1 Torr. The rate constant data (k(1) and k(2) at different temperatures) were used to derive the Arrhenius expressions, k(1) = (1.5 +/- 0.7) x 10(-10) exp[(-281 +/-138)/T] cm(3) molecule' S-1 and k(2) = (1.6 +/- 0.4) x 10(-9) exp[(-884 +/- 69)/T] cm(3) molecule(-1) s(-1). At 298 K and 1 Torr, the products of both reactions have been studied. Reactions I and 2 have been found to proceed through an abstraction mechanism, leading to HCl + C5H9(O) and HCl + C6H11(O), respectively. The branching ratio for the abstraction channel was determined at 298 K and 1 Torr, as 0.97 +/-0.10 for reaction 1 and 0.98 0.08 for reaction 2. The results obtained are related to previous studies, and the mechanism and atmospheric implications for both reactions are discussed.