Sixteen unselected untreated patients with primary myelodysplastic syndromes (MDS) and various combinations of blood cytopenia were treated with danazol, an attenuated androgen reported to be of some value in these conditions. After a 12 week trial (danazol 600 mg/day/p.o.), anaemia improved in 4/14 patients, with transfusional requirements being reduced by 50% or more in four other cases (response 57%). An enhanced reticulocyte production was documented in 6/13 cases (46%), and thrombocytopenia resolved in 5/8 (62%). Results of the granulocyte count were less satisfactory, with only one partial response obtained among five cases. A normalization of the monocyte count was seen in 3/5 patients with chronic myelomonocytic leukaemia, with one of them achieving a complete haematological and clinical remission lasting 6 months. Circulating blast cells decreased significantly (50% or more) in 4/6 cases. Although clinical symptoms from anaemia and bleeding disappeared in responsive cases, four patients developed acute non-lymphocytic leukaemia. Danazol was well tolerated and produced no acute or chronic toxicity. The drug appears useful in the management of anaemic and thrombocytopenic MDS patients.