Abstract: When determining the bubble point or the largest pore of a membrane or of a filter material, the membrane or the filter material is placed in a container, with the membrane or the filter material thus dividing this container into two compartments. Then, the first compartment is filled with gas, and the second compartment and the pores of the membrane (or the filter material) are filled with a wetting liquid. The pressure in the gas compartment is raised at least until the gas displaces the liquid from the largest pore. The bubble point is defined by means of the gas-compartment pressure then prevailing, or the cross-sectional dimension of the largest pore can be calculated. According to the invention, the gas-compartment pressure corresponding to the bubble point is determined by measuring a sudden increase in the sound intensity in the liquid compartment. The measurement of the sound intensity is preferably carried out in the ultrasonic range.