A pilot study was carried through to assess the reproducibility of a new method of measuring breast volume. Twenty healthy female volunteers participated. A negative replica of the breast was made with thermoplastic cast material. The volume was measured by filling the cast with water until it reached two opposite points of the boundaries of the breast delineated on the cast. Three measurements were made of every cast and the mean was calculated. The range of the three measurements expressed as a percentage of the mean volume was 2.9 (SD 1.6)%. Each volunteer's breasts were measured twice with a brief intervening pause. The coefficient of variation between the two corresponding measurements was 6%.