We investigated the frequencies of early populations of progenitors in aplastic anaemia (AA) bone marrow, from patients with a range of disease severity, compared with normal. Double-colour immunofluorescent staining for CD34 and CD33 was carried out on bone marrow mononuclear cells (BMMC) and analysed using fluorescence activated cell sorting (FACS). AA CD34+ cells were reduced by 68% compared to normal. In addition, AA CD33+ cells and the three progenitor subsets (CD34+/CD33-, CD34+/CD33+ and CD34-/CD33+) were reduced by 44-80%. Our data lend further support for an early stem cell deficiency in AA.