The isospin degree of freedom of the pairing force is studied in the framework of the rotational (Δ 0) and vibrational (Δ=0) models. The magnitude Δ is the BCS gap parameter. The predictions of the two models concerning two-nucleon transfer reactions and energy levels are compared and contrasted. Some of the available experimental material around Ni56 is discussed in this framework. Further experiments are suggested which would help decide between the coupling schemes.