Optical resolution of 4,4,4-trifluoro-3-(indole-3-)butyric acid (TFIBA), a novel plant growth regulator, was achieved by Pseudomonas fluorescens lipase (lipase AK)-catalyzed enantioselective hydrolysis of its trifluoroethyl ester. Compared with the reactivity of lipase AK for TFIBA ethyl ester, that for TFIBA trifluoroethyl ester was markedly increased, and the reaction was complete within Ih at 40 degrees C in phosphate buffer containing 10% tert-amyl alcohol. The reactivity of lipase AK for TFIBA trifluoroethyl ester was similar to that for two other TFIBA esters (fluoroethyl and difluoroethyl), and higher than that for other esters (chloroethyl, trichloroethyl, and tribromoethyl). These results suggest that the introduction of fluorine atom(s) into an alcoholic group is an effective way to increase the rate of hydrolysis by lipase AK.