The separation of gases and liquids under microgravity conditions is a common task to be accomplished in Life Support Systems of Spacecraft. Separation has to be achieved in two main domains: water separators separate water from an air stream coming e.g. from the slurper holes of a condensing heat exchanger gas traps have to safeguard sensitive devices in water loops, like e.g. centrifugal pumps or passages with small inner diameter, against blockage by gas bubbles.This paper describes the evaluation of a two-membrane concept fur use in microgravity. The concept originally had been developed for medical application and features a hydrophilic screen for retaining gas bubbles in a water stream; the bubbles are then vented via a hydrophobic membrane to the ambient.Commercial blood gas bubble filters were successfully tested in parabolic flight proving the feasibility of the concept for application as gas trap in microgravity. Furthermore the tests showed a potential of the concept for water separation from air. A Life test indicated sufficient stability of the membranes during three months. Pressure drops were found to lie in acceptable ranges for the envisaged applications.The paper describes the functional principle of the membrane filter and obtained experimental results and discusses possible applications in microgravity.