Inositol 1,4,5-trisphosohate (IP3) and its receptors play a pivotal role in calcium signal transduction in mammals. Some fractions of tonoplast and endoplasmic reticulum membranes have high affinity binding activity for IP3, and IP3 can induce Ca2+ release in several plants. However, no homologues of mammalian IP3 receptors have been found in plants. In this study, we isolated the microsomal fractions from rice cells in suspension culture and further obtained putative IP3-binding proteins by heparin-agarose affinity purification. The IP3 binding activities of these protein fractions were determined by [3H]IP3 binding assay. SDS-PAGE and MS analysis were then performed to characterise these proteins. We have identified 297 proteins from the eluates of heparin-agarose column chromatography, which will provide insight into the IP3 signalling pathways in plants.