The FFC ceramics(TM) from FFC Japan Co., Ltd. are now widely used in the fields of agriculture, fishery and food industry in Japan. Recently the FFC ceramic beads-based technology has been also applied to meet several environmental problems including pollution in sea, lakes and rivers. In this study the FFC ceramic water was tested for effect on plant enzyme, potato apyrase (EC 18.104.22.168; ATP-diphosphohydrolase), which hydrolyses nucleoside triphosphate (NTP) and -diphosphate (NDP) to produce corresponding nucleoside monophosphate (NMP) and inorganic phosphate (Pi). Addition of the FFC ceramic water to the enzyme reaction mixture markedly enhanced ATP-hydrolyzing activity, when used as ATP as substrate. However, the concomitant presence of Ca(2+) chelator, EGTA (O,O'-bis(2-aminoethyl)ethyleneglycol-N,N,N',N'-tetraacetic acid) with the FFC ceramic water, completely abolished the enzyme activation. In fact, exogenous calcium ion such as CaSO4 mimicked the FFC ceramic water. These results indicate that apyrase activation by the FFC ceramic water largely depends on calcium ions. On the other hand, when the FFC ceramic water prepared from "used" ceramics was tested for the apyrase activity, the enhanced effect on apyrase was decreased compared to the FFC ceramic water from "new" ones. This result, consistent with our present data covering concentration of calcium ions and conductivity, indicates that long and/or successive usage of the ceramic beads results in decrease of contents of released minerals, especially calcium ions. The apyrase-based enzyme assay presented here is probably applicable to estimate and quantify the effect of FFC ceramic water.