Abstract We introduce a Sciuto-Della Selva-Saito type vertex describing the emission of two reggeons from the world-surface of the bosonic string. This so-called dual vertex is written in terms of two complete string fields; one physical, representing the pair of external reggeons and one auxiliary associated with the world-surface. The dual vertex has therefore a structure quite different from that of the product of two ordinary Sciuto-Della Selva-Saito vertices, being instead, as we demonstrate, dual to it. Some properties of the dual vertex are presented and the construction of it is described in some detail. We also briefly discuss the importance of this kind of vertex when generalized to the NSR string.