The treatment of pairing interactions in systems with a finite number of particles, like the atomic nucleus, was originally performed by applying the BCS transformations in the energy representation. An alternative method, formulated by de Gennes, introduces explicitly the radial dependence of the BCS-type solutions of the pairing force problem for superconductors. In this paper we explore the consequences of the use of de Gennes's formalism to calculate the pairing contribution to two-nucleon transfer amplitudes.