Equimolecular mixtures of esters of long-chain fatty acids and short-chain primary alcohols are hydrolysed by pure porcine pancreatic lipase, and the composition of the acyl chains in the liberated fatty acids is compared to that of initial esters mixtures. This gives the relative lipolysis rates of esters in which the alkyl groups are different. Methyl esters are cleaved by lipase 5 times faster than ethyl esters. The relative hydrolysis rates remain rather slow for esters of C 3 and C 4 alcohols; they increase abruptly for esters of n-hexyl alcohol, which are, in fact, cleaved faster than methyl esters. The results are compared to those that had been previously observed with rat pancreatic juice; they are discussed in relation to a possible enzyme specificity and to the orientation of ester molecules at an oil-water interface.