There has been some dispute in the literature as to the sensitivity of the zinc indicator FluoZin-3 to calcium, with suggestions that physiological levels of calcium and magnesium effectively occlude the response of the probe to zinc. In this communication we demonstrate that calcium concentrations as high as 10 mM do not prevent FluoZin-3 from detecting zinc elevations as low as 100 pM. Moreover, the inclusion of a few microM Ca-EDTA does not prevent FluoZin-3 from responding to increases in zinc concentration but does extend the dynamic range of the probe by reducing contaminating zinc levels and allowing the probe to respond to multiple zinc additions. In addition, we have derived a mathematical model to account for the kinetics of FluoZin-3 response to zinc in the presence of an additional zinc and calcium chelator.