A highly sensitive method aimed at detection of CsCl on nuclear remediation sites with isotopic selectivity was developed. The approach couples electric discharge in hydrogen as a source of dissociation of CsCl with high-resolution absorption spectroscopy using a tunable laser diode for subsequent identification of metallic cesium. The number densities of CsCl as low as 5 × 107 cm-3 can be detected with a signal-to-noise ratio better than 10 during seconds-long observation.