A new benzothiazolyl functionalized ionophore based upon the cafix[4]arene-crown-5 ether has been prepared and its fluoroionophoric properties toward Ca2+ ions were investigated. The compound exhibited a pronouncedly selective fluoroionophoric behavior toward Ca2+ ions were among those surveyed physiologically important metal ions of Na+. K+. and Mg2+. Detection limit for Ca2+ ions was found to be 9x10(-5) M in dioxane water (80:20. v.v) solution. (C) 2002 Elsevier Science Ltd. All rights reserved.