Apyrase activities in some tissues and cells, such as peripheral vascular endothelial cells, have been reported, but these in endocardium endothelial cells have not been reported. The present study was to characterise the properties of bovine endocardium endothelial cells (BEEC)-associated apyrase. Apyrase activity was assayed by inorganic phosphate release, which could be inhibited concentration-dependently by NaN3, an apyrase inhibitor. NaF (20 mmol/L), another inhibitor of apyrase, also markedly inhibited the activity. EDTA or EGTA (1 mmol/L) could also inhibit the activity completely. However, the inhibitor for Na+/K(+)-ATPase, ouabain (3 mmol/L) did not affect the enzyme activity. BEEC apyrase activity was dependent on divalent cations (Ca2+ or Mg2+) and pH value.