This study examines the effect of in vitro exposure to enzymes on the performance properties of Biomer, a segmented polyetherurethane used in a number of blood-contacting devices such as catheters, heart assist pumps, and chambers for artificial hearts. The ultrathin samples were treated with two proteolytic enzymes, papain and urease, for periods of 1-6 months at 37 degrees C. The treated Biomer samples were subjected to chemical and physical analysis. Effects of biodegradation by the enzymes were assessed by fatigue tests, gel permeation chromatography (GPC), and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) analysis. Papain was found to be more effective in degrading the polymer than urease. Mechanisms for enzymic degradation are proposed.