We studied relatives of adult patients with acquired aplastic anaemia. Eight patients were found to have 11 family members with peripheral blood pancytopenia. Six of the 11 affected relatives had diminished and four normal cellularity and one had hypercellularity of the bone marrow. Thus, 19 persons in these eight families were affected. In two families, father and son were affected, in four families brother and/or sister, in one family a brother and an aunt and in one a nephew of the index patient. None of the patients or family members had congenital defects. All patients were diagnosed at an adult age and, furthermore, also the mode of inheritance in some of the families seems to exclude Fanconi's syndrome. It is concluded that relatives of patients with aplastic anaemia should be screened for manifestations of this syndrome of familial acquired blood pancytopenias.