An optical sensor for the direct measurement of silver was developed. The basic element of this optode is the immobilization of diphenylthiocarbazone on a triacetyl cellulose membrane. This optode has a linear range of up to 40 mu g mL(-1) of Ag+ ions, with a limit of detection of 0.01 mu g mL(-1). The response time of the optode was 4-7 min, depending on the concentration of Ag+ ions.