SummaryThe clinical course and the haematologic events in a patient suffering from metastatic thyroid cancer after administration of 806 mCi of 131I are described. A serious bone marrow depression developed and was treated successfully. The haematological changes during the early and late phases of the radiation injury were studied in detail and compared with those after external irradiation. The haematological events after internal irradiation with 131I are characterised by initial neutrophilic leukocytosis, protracted lymphopenia, slowly developing anaemia reaching lowest values about 3 months after administration, erythroid hyperplasia in the bone marrow after recovery from bone marrow depression and prominent cytological features of the bone marrow, especially pronounced erythropoietic polyploidy.
