The effect of overexpression of heat shock protein (HSP)72 on apoptosis induced by different stimuli in human umbilical vein endothelial cells (HUVECs) and the angiogenic cell line, ECV304, was studied. Transient overexpression of HSP72 was achieved using an adenoviral vector (Advhsp72) and apoptosis was induced by heat shock, tumour necrosis factor (TNF)-alpha with cycloheximide (CHX), lipopolysaccharide (LPS) with TNF-alpha and verocytotoxin (VT). Apoptosis induced by heat shock was reduced by HSP72 expression. However, HSP72 expression in HUVECs increased apoptosis induced by TNF-alpha/CHX, LPS and VT measured by flow cytometric analysis of propidium iodide (PI)-stained permeabilized cells. In contrast, apoptosis in ECV304 induced by the same stimuli was reduced by HSP72 expression. No difference was seen in cells transduced with a control adenoviral vector expressing beta-galactosidase. These data imply that induction of HSP72 in cells modulates responses to apoptotic stimuli, but that the nature of the response varies with the cell type. However, it is clear that in situations where apoptosis may be part of a pathological process, HSP72 induction, for example by reperfusion injury, may exacerbate the process.