The total rates of reaction between four cyclic esters (beta-butyro-, gamma-butyro-, gamma-valero- and delta-valero-lactones) and the OH radical have been measured relative to the rate of reaction of a reference compound, ethene, at room temperatures. The measurements show that the rates increase with increasing ring size. Theoretical calculations on the four lactones with the inclusion of a fifth, alpha-methyl-gamma-butyrolactone, are broadly in agreement with this picture but provide a more insightful view of the sites at which hydrogen atom abstraction occurs in each molecule.