51Cr-platelet kinetic studies were performed in 77 patients with idiopathic thrombocytopenic purpura. The sequestration site was splenic for 63, splenic/hepatic for 7 or hepatic for remaining 7 patients. In 20 patients platelet survival was extremely shortened to 0-3 h, whereas only 26 patients had a survival time of more than 24 h. Those patients with low platelet counts also had a very short platelet survival time, whereas patients with higher platelet counts (greater than 50 x 10(9)/l) had longer platelet survival times. 51 patients (66%) were splenectomized following the kinetic studies. 25 patients who had a splenic sequestration site had normalized platelet counts and 6 patients had platelet counts between 80-149 x 10(9)/l 12 months after splenectomy (i.e. in 92% of cases with splenic sequestration site a full or partial remission). Of the 11 patients with a hepatic or splenic/hepatic sequestration site, 2 patients had full remission, 1 partial remission, 3 patients had minimal improvement and 5 other patients were treatment failures in respect to the splenectomy.