Five strains mere isolated from soil as fungi able to degrade both poly(3-hydroxybutyrate) (PHB) and polycaprolactone (PCL), and one of the strains, D218, identified as Paecilomyces lilacinus, was selected. In 10 d, D218 degraded PHB almost completely and 10% of the PCL, each at 0.1% in the culture media. Strain D218 excreted PHB and PCL depolymerases in media containing either PHB, PCL or PHB plus PCL. Both depolymerase activities were reduced when the medium was supplemented with either soluble starch, lactase or glucose. The optimum conditions for PHB depolymerase were pH 6.5 to 7.5 at 50 degrees C, while those far PCL depolymerase were pH 3.5 to 4.5 at 30 degrees C. In the reaction mixtures used for the enzyme assays, the formation of 3-hydroxybutyrate from PHB and epsilon-caprolactone from PCL was confirmed by high performance liquid chromatography.