Lithium is quantitatively precipitated as a complex periodate by a strongly alkaline potassium periodate solution. Such a solution may be made the basis of selective methods for the detection or determination of lithium, since with proper adjustment of alkalinity the other alkali metals do not form insoluble periodates. By systematic experiments with a series of trial reagents it was found that a reagent of the following composition gave the best results: potassium hydroxide, 24 grams; potassium metaperiodate, 10 grams; water, 100 ml.