The E2F family of transcription factors are thought to play an important role in the control of cell cycle progression. There is now also increasing evidence that some family members may act as oncogenes or tumour suppressor genes. The characterization of these proteins in human primary haemopoietic cells and acute myeloid leukaemia (AML) blasts may thus give an insight to the molecular mechanisms governing proliferation and leukaemogenesis in these cells. Therefore we analysed the expression of E2F-DNA binding activity and the constituent proteins found in the complexes in human primary haemopoietic cells of various lineages. We also studied blasts from 18 patients with acute myeloid leukaemia (AML). On electromobility shift assays (EMSA) a single E2F-DNA binding complex was detected in T cells, B cells and monocytes which was shown to contain E2F-4, DP-1 and p130, indicating that all quiescent haemopoietic cells have the same complex. Examination of 18 AML samples by EMSA revealed the presence of E2F binding and no gross abnormalities were detected. An E2F-4/p130 complex was detected in representative samples of all FAB types analysed. Thus abnormalities of E2F function are unlikely to play a primary pathogenic role in AML.