A beta attenuation method has been developed for measuring void fractions which is sensitive enough for use during local boiling. Comparisons are made with gamma attenuation methods, the effects of preferential void location are demonstrated, and typical void fractions measured during forced-convection, subcooled boiling of water are presented. The technique has been found to be readily applicable to the accurate determination of void fractions during either saturated or subcooled boiling of water and organic liquids.