The stereoselectivity of porcine pancreas lipase (PPL) was investigated during the enzymatic hydrolysis of triolein and its partial glycerides in the presence of supercritical carbon dioxide (SCCO2) as reaction medium. The water content of the immobilized lipases was varied. The partial glycerides were separated into mono- and diglycerides by TLC, converted to their 3,5-dinitrophenylurethane derivatives and subsequently resolved into sn-1,2 and sn-2,3 enantiomers (estimation of dioleins) or into sn-1 and sn-3 enantiomers (estimation of monooleins) by HPLC on a chiral stationary phase (Sumichiral OA-4100). In all reactions under the conditions employed, PPL revealed a distinct preference for the sn-3 position of the glycerol. However, the stereoselectivity depends on the reaction time, the substances initially used and the enzyme water content. It seems that the effect of the enzyme water content on the activity and selectivity of porcine pancreas lipase in SCCO2 is based on a modification of the "micro-environment' of the enzyme by the solution of CO2 in water, causing a decrease of the pH value.