The significance of the site of platelet sequestration in determining the indication for splenectomy in idiopathic thrombocytopenic purpura (ITP) is a controversial subject. However, most of the negative conclusions are based on 51chromium labelling of homologous platelets. We report here the results of an analysis of 222 cases in which the kinetic study of 111indium-oxinate-labelled autologous platelets was performed under homogeneous technical conditions. 103 of these patients subsequently underwent splenectomy. This study demonstrates that the site of platelet sequestration in active ITP constitutes a variable independent of the patient's age, history of the disease and its severity (platelet count, lifespan). The sequestration site is a good predictive element of the short-term efficacy of splenectomy (71/76 cases with splenic sequestration obtained a platelet count exceeding 100 x 10(9)/l versus 7/13 cases with mixed sequestration and 1/14 cases with hepatic sequestration), and the long-term results (6 months to 5 years after splenectomy) do confirm the clinical value of this study.