Considering the important role played by enzymatic hydrolysis in the metabolism of therapeutic agents designed by retrometabolic approaches (soft drugs and chemical delivery systems), the present article offers a review of a number of issues related to the enzymatic hydrolysis of carboxylic esters. Current knowledge regarding interorgan- and interspecies variability, stereospecificity, activation energy, proposed mechanism, and quantitative structure-metabolism relationship is summarized. The effects of chain-length and branching in the alcohol or acyl substituent on the rate of hydrolysis in congener series are also summarized. Available in vitro human blood data suggest that shortest half-lives are achieved with sterically non-hindered chains that are neither too short nor too long and are of around four carbon-atom long.