Two different types of amphiphilic polymers were used as surface-modifying additives to a polyetherurethane, Pellethane 2363-75D, which has T-g close to room temperature. The additives used were a segmented polyetherurethane designated Pol C, and Pluronics PE6800 and PE9400, i.e., triblock copolymers of propylene oxide and ethylene oxide. Pol C was prepared from poly(ethylene glycol), methylene diphenylene diisocyanate, and a fatty acid monoglyceride. The properties of the blends were investigated in their unhydrated state and after water immersion at 23 degrees C and 80 degrees C. Surface composition, water absorption, and leakage of additives to the aqueous phase have been studied. From ESCA and contact angle measurements it was concluded that Pol C was enriched in the surface layer of the matrix material after water immersion at 80 degrees C. The Pluronics showed less effects on the surface properties of the matrix material, probably because of their high water solubility.