We report on a patient with myelodysplastic syndrome (MDS), classified as refractory anaemia with excess of blasts-2, and histiocytoid Sweet's syndrome. The skin lesions disappeared after initiation of corticosteroids and doxycycline. Remarkably, two months later a complete remission of the MDS occurred. Fourteen months later both the skin lesions and the MDS relapsed. Antileukaemic activity following reversion of the impaired cellular immunity due to an increased number of natural killer cells in his bone marrow may be responsible for this rare event. Inhibition of T-cell mediated myelosuppression by corticosteroids or a proapoptotic effect of doxycycline may have attributed as well.