The fluoride ion-selective electrode has been widely used recently for the determination of metal ion-fluoride stability constants. Previously, it has been reported to be less sensitive, although more convenient, than the well established Fe(III)/Fe(II) method of detection of fluoride complexes. Earlier work indicates this conclusion to be valid for strong fluoride complexes, however, for weak complexes it would appear from the present study that the fluoride electrode may be substantially superior in convenience, sensitivity and accuracy. Data are reported for the sparingly soluble group (II) fluorides of Mg, Ca, Sr and Ba to demonstrate the reproducibility of the fluoride ion electrode for detection of weak complexes. Calculations are given to show that the lower limit of stability constant detectability with this electrode is approximately 0·2 mole-1l. for 1:1 complexes.