Bone marrow aspirates were obtained from the right or left posterior superior iliac spine of 50 healthy volunteers, 30 men and 20 women. Reference ranges were derived for each cell type and for the myeloid:erythroid (M:E) ratio. The M:E ratio and the percentage of neutrophils were significantly higher in the women and the erythroid component significantly lower. All 28 evaluable men and 11/17 evaluable women had storage iron present in more than trace amounts. The percentage of erythroblasts with detectable iron granules varied very widely, from 3% to 69% in those with more than a trace of storage iron. Minor dyserythropoietic features were present in a high percentage of subjects and 19/50 subjects had one or two dysplastic megakaryocytes. Granulocytic dysplasia was not detected.