Abstract: The indicator compounds of the present invention are substituted or unsubstituted BAPTA-type chelators that contain a benzazolyl-coumarin substructure, and the pharmaceutically acceptable non-toxic salts and esters thereof. These compounds are useful for the detection and quantification of polycationic metal ions, particularly Ca.sup.2+.The compounds of the invention have the core structure ##STR1## or the structure ##STR2## where m=2 or 3 and X can be S, O, or C(CH.sub.3).sub.2. The above core structures are optionally substituted by substituents that alter the binding affinity of the indicator, shift the spectral properties of the indicator, or act as a reactive site for the preparation of a variety of conjugates.