The enzymatic resolution of racemic glycidyl in supercritical CO2 is described. The enzymatic route chosen was the esterification with butyric acid catalyzed by either free or immobilized pol cine pancreatic lipase. The solubility of glycidol, the least soluble reactant, was measured in CO2 at 35 degrees C and pressures in the range 70-180 bar for concentrations of butyric acid up to 500 mM. The pressure selected for subsequent experiments was 140 bar. The partitioning of water between CO2 and the enzyme preparations was quantified for various amounts of added water. The experimental sorption isotherms obtained were used to derive the water content of the enzyme preparations assayed in kinetic studies. For the free enzyme, maximum reaction rates were obtained for an enzyme water content of 10 +/- 2% w/w, the same as in organic solvents, although the corresponding initial rate of 0.0045 +/- 0.0003 M h(-1) g(-1) was much lower than for these solvents. A series of supports covering a wide range of hydrophilicitiesd for enzyme activity, the best results being for the more hydrophilic ones, Sephadex G-25 and Bio-gel P6. Enzyme immobilized on these supports performed better than the free enzyme, leading to optimized initial rates of 0.0110 +/- 0.0007 M h(-1) g(-1) and enantiomeric purities of 83 +/- 2% of (S)-glycidyl butyrate, atenzyme preparations. The selectivity observed is the same as the highest value obtained in organic solvents. As in those solvents, enantioselectivity in CO2 does not depend on enzyme hydration.