In 45 beta-thalassaemia heterozygotes and in 38 normal controls we determined by ultrasound tomography: (a) the surface of the projection of the spleen to thoracic and abdominal wall, (b) the maximum diameters of the organ, and (c) its volume. The volume of the spleen is significantly bigger in heterozygotes as opposed to normals (132.94 +/- 41.76 and 80.29 +/- 25.88, respectively). In 17.8% of heterozygotes a palpable spleen was found. The findings of this study lead to the hypothesis that in all heterozygotes the final volume of the organ is increased; however, in only 17.8% of them a palpable spleen is found.