D-myo-Inositol-3,4,5,6-tetraphosphate (sodium salt) (Ins(3,4,5,6)-P4) is one of several different inositol oligophosphate isomers implicated in signal transduction. It almost completely inhibits calcium-activated chloride channels at a concentration of 8-10 µM. Related inositol oligophosphates Ins(1,3,4,5)-P4, Ins(1,3,4,6)-P4, Ins(1,4,5,6)-P4, and Ins(1,3,4,5,6)-P5 do not inhibit the calcium channel at concentrations up to 100 µM. Ins(1,3,4)P3-mediated inhibition of Ins(3,4,5,6)-P4 1-kinase increases the cellular level of Ins(3,4,5,6)-P4, thus regulating channel inhibition. Ins(3,4,5,6)-P4 was found to be inactive when analyzed for Ca2+-releasing potency in Xenopus oocytes.