THE determination of sulphydryl groups in protein by amperometric titration in neutral aqueous solution has been reported by Benesch, Lardy and Benesch1. The use of this method for the estimation of glutathione in animal tissue has been considered in detail by Thomson and Martin2. One disadvantage of this amperometrie titration technique is the transient life of the agar–salt bridge which connects the reference electrode to the reaction vessel containing the rotating platinum electrode. This communication describes a modification of the technique in which the agar–salt bridge is replaced by a ceramic plug which permits direct contact between the reference electrode and the reaction solution. In addition to this, the use of a motor which rotates the platinum electrode at a constant speed has given improved reproducibility of the galvanometer deflexion.