The determination of Cl- in plant tissues was investigated by FeSCN2+ spectrophotometry following SCN- displacement from Hg(SCN)2 by Cl-. The calibration curve was nonlinear, but consistent and reproducible. As little as 10 nmol Cl- could be measured. There was no obvious interference in color development by water-soluble components in plant tissues. Values obtained by this method were in close agreement with those obtained potentiometrically and by coulometric titration.