The authors describe three cases of refractory anaemia with an excess of myeloblasts in the bone marrow (RAEM), associated with pyoderma gangrenosum (PG) and vasculitis. The first patient was an 85-year old man whose RAEM had begun in 1979. In 1985, he developed pyoderma gangrenosum in the popliteal fossa and on the right heel. Histology confirmed the diagnosis. A direct immunofluorescence test on the biopsy specimen was negative. Apart from the haematological syndrome, there were no laboratory abnormalities. The cutaneous lesions disappeared after 7 weeks of treatment with prednisolone 20 mg per day. The blood disease remained unchanged. The second patient was a 71-year old woman with RAEM since 1982. In 1984, she presented with lesions of cutaneous vasculitis located on the anterior aspect of the upper third of her left leg. There was neither arthralgia nor fever, and no history of drug toxicity or infection. Beside RAEM, polyclonal hyperglobulinaemia was present. Histological examination of the skin showed evidence of vasculitis with fibrinoid necrosis of vascular walls and perivascular lympho-histiocytic infiltrate with granulocytes and slight leucocytoclasia. Direct immunofluorescence testing of the skin demonstrated intravascular complement deposits. There were no circulating immune complexes; measurements of complement and complement fractions gave normal values; no cryoglobulin was found. The cutaneous lesions recurred on two occasions in 6 months, although no drug toxicity or infection could be elicited and the haematological syndrome was unaffected. The third patient was a 67-year old man with RAEM since 1982. In 1983, an ulcero-necrotic lesion spontaneously developed on his right leg.(ABSTRACT TRUNCATED AT 250 WORDS)