It is proposed to develop a fiber optic probe for lithium ion based on new fluorescent lithium ion carriers immobilized on fiber optic bundles by Langmuir-Blodgett film techniques. In Phase I the new fluorescent ionophore will be synthesized and tested for Li/Na specificity. Optical properties will also be investigated to determine suitability for use in a fiber optic probe. Following, some additional analog of the flourophores prepared in Phase I will be synthesized. Those having the best specificities and optical properties for lithium will be used to prepare fiber optic probes. The probes will be used to develop a method for determination of Li+ ion in the blood serum of patients being treated with lithium for manic/depressive psychosis. Immediate application of the lithium ion sensor is in an inexpensive instrument for determination of Li+ in the blood of manic/depressive patients using Li therapy. The use of L-B films as a means of immobilizing specific fluorescent chelator will have much broader application in the preparation of ion sensors for other metal ions.