The effect of structural variations on the rates of elastasecatalyzed hydrolysis of model carbonate and carbamate esters was studied using HPLC. It is shown that branching in the immediate vicinity of the carbonate or carbamate functionality results in decreased hydrolysis rates. Whereas aryl carbonates act as substrates for elastase, p-nitrophenyl butyl carbamate inhibits the enzyme. A novel method was developed for the entrapment and quantitation of 14C02 produced upon hydrolysis of carbonyl-14C-labeled carbonate esters. This technique could be useful in studying the mechanism of enzymatic hydrolysis of this type of compound and has the potential of being adapted as a convenient method in the assessment of esterolytic activity of tissue homogenates.