The enhancement factors for the solute diffusion in dilute b.c.c. alloys are discussed on the lines of two approaches. One of them is based on the Taylor’s expansion series of activation energy and pre-exponential factor on concentration. The convergency of these series is studied. The second approach is formulated in the framework of the statistical theory. The comparative analyses of these two ways for the explanation of the enhancement of diffusion is carried out. The concentration dependencies of jump frequencies are investigated for V-Zr dilute solid solution as an example. It is shown that these dependencies are connected with the changes of the migration energy E(m)(c) as well as with the changes of the frequencies of vibrations. Different mechanisms that are possible for the explanation of the enhancement of D(c) are discussed.