Technetium-99m scintigraphy of the spleen was performed in 32 patients with various haematologic disorders prior to splenectomy. From the gamma camera image of the spleen, the weight of the spleen was estimated using two different mathematical formulas, and the results obtained were compared to the postoperative spleen weight. Both formulas revealed spleen weights showing highly significant correlations to the postoperative spleen weight and with similar standard deviations. Visual evaluation of the scintigram by an experienced examiner with classification of the spleens into four groups according to spleen weight revealed results as good as the mathematical calculations in predicting the postoperative spleen weight, both techniques giving diagnostic specificities of 0.70–0.80 for all groups and diagnostic sensitivities of 0.80–1.00. Physical examination of the abdomen showed that about 50% of the spleens weighing between 250 and 1,000 g were not palpable. Therefore, it is concluded that physical examination of the abdomen alone is unreliable. Radioisotope scintigraphy of the spleen is recommended, this method being fast, with negligible discomfort to the patient, and with sufficient accuracy for daily clinical work.