259 patients with primary proliferative polycythaemia (PPP) and idiopathic thrombocythaemia (IT) have been treated with 32P over the last 15 years. Complete follow-up data were obtained in 238 patients. PPP was the diagnosis in 183 patients and 76 patients had IT. The sex ratio in PPP was male/female 1.1:1 and in IT 1:1.4. Patients' ages ranged from 28 to 95 years (median 72 years). The number of 32P administrations per patient ranged from 1 to 13 (median 2) and the total administered activity per patient ranged from 81.4 to 4162 MBq (median 496 MBq). The outcome showed a normalization of the full blood count in 50% of patients after a single administration of 32P and in 73% after two treatments. 13 patients (5.5%) developed myelofibrosis; 18 (7.6%) developed leukaemia while other cancers arose in 19 patients (8%). 32P therapy proved to be of particular value in the elderly. 32P is easy to administer and is cost effective, compared with the alternative of chemotherapy where good compliance and frequent hospital visits are required.