An impedance type void meter is described which is suitable for measurement of void-fraction in air-water and steam-water mixtures. The mechanical construction of the meter differs from those previously described in that it minimises problems with pressure casing penetrations and with sealing of connecting leads. A condensed theoretical analysis of the behaviour of the meter in air-water mixtures is included, together with a discussion of possible errors due to changes in conductivity of water and excitation frequency. Two different systems on electronics are described, a series and a bridge type system. An experimental calibration of the prototype meter by the "quick-closing valves method" is compared with the theoretical response and the disagreement arising from comparison is explained.