Apparatus for removing air bubbles from blood and from a dialysate solution are described herein. In one cassette-style embodiment of a blood debubbler, the debubbler includes front and rear covers, a fluid circuit board between the front and rear covers and defining a blood chamber between the fluid circuit board and the front cover and an air chamber between the fluid circuit board and the rear cover, and a microporous membrane separating the blood chamber from the air chamber. A support means is provided for supporting the microporous membrane from the air side of the membrane. A pressure sensor is provided within the front and rear covers for measuring the blood pressure in the blood chamber. The debubbler has a blood inlet port and a blood outlet port for conducting blood to and from the blood chamber. An air port is provided in communication with the air chamber, which allows for air passing through the microporous membrane to escape.