Thioamide derivative with a pyrene fluorophore was smoothly transformed to its corresponding amide by Zr4+ ions in the presence of hydrogen peroxide. The transformation was evidenced by H-1 NMR spectroscopy and the signaling was completed within 10 min after sample preparation. Interference from Ag+ and Hg2+ ions in Zr4+-selective fluorescence signaling was readily suppressed with the use of Sn2+ as a reducing additive. Discrimination of Zr4+ from closely related hafnium, which is a frequent contaminant in commercial zirconium, was not possible. Prominent Zr4+-selective turn-on type fluorescence signaling was possible with a detection limit of 4.6 X 10(-6) M in an aqueous 99% ethanol solution.