Dithizone immobilized on XAD-4 resin has been studied as a sensor element of an optical sensor for lead using a flow-cell. Using this arrangement, lead in solution has been determined in the concentration range 1 x 10(-5)-3 x 10(-7)M with a detection limit of 1 x 10(-8)M (i.e., 2 mug/l.). The standard deviation of the method for the measurement of lead at a concentration of 1 x 10(-6)M was found to be 7%. The response of the sensor was reproducible and can be regenerated using 0.01M hydrochloric acid followed by citrate-hydroxylamine solution.391114991503