The granulocytes of 9 patients with Down's syndrome (DS) were examined for morphological abnormalities. Electron microscope examination showed abnormalities in the nucleus, such as pockets, bridges, appendices and fibrillar bodies in 25–57 % of the cells as compared to similar, but less conspicuous findings in 5–10 % of the granulocytes of 5 controls. The similarity of these ultrastructural malformations to those described in different forms of leukaemia is stressed. Since chromosomal abnormalities exist in both DS and leukaemia, the possibility that they are the cause for the ultrastructural alterations is discussed.

A patient with clinical and haematological findings compatible with congenital dyserythropoietic anaemia (CDA) most probably type I1 is described. In contradistinction to previous observations, electron microscope examination of the erythroid cells in the bone marrow showed the concomitant appearance of nuclei at different maturation stages in a single cell. In addition, a marked tendency toward multinuclearity of the megakaryocytes was found. The mature erythroblasts showed an increased uptake of 3H-uridine, while the proerythroblasts revealed an uptake of 3H-thymidine less than is normally found in these cells. Thes findings suggest an impairment in RNA and DNA synthesis.