Possible mechanisms are considered for the transfer of electronic excitation energy in collisions between an excited alkali atom MA*(2Pj) and an unexcited atom MB(2S1/2). It is shown that a dipole–dipole interaction which is responsible for the transfer of electronic excitation energy in collisions between identical partners (MA = MB) is not sufficient to explain the observed magnitudes of the cross sections and that, therefore, the exchange interaction can no longer be neglected. If the exchange interaction is taken into account, it can be shown that there are regions of nonadiabaticity in the energy diagram, which are probably responsible for the change in the electronic energy states of the collision partners. The calculated cross sections are compared with experimental values.