Farnesol preferentially inhibits proliferation and induces apoptosis of tumour-derived but not non-transformed cell lines. We investigated whether farnesol induces apoptosis of blasts from patients with acute myeloid leukaemia (AML) and leukaemic cell lines, as compared with normal, human primary haemopoietic cells. We show that 30 microM farnesol causes apoptosis of leukaemic cell lines of T- and B-lymphocyte, myeloid or erythroid lineages and primary blasts obtained from patients with AML. However, the same concentration did not kill primary monocytes, or quiescent or proliferating T-lymphocytes. We conclude that farnesol selectively kills AML blasts and leukaemic cell lines in preference to primary haemopoietic cells.