  In the paper " Superconducting decay length in a ferromagnetic metal" by
Gusakova, Kupriyanov and Golubov [Pis'ma v ZhETF 83, 487 (2006);
cond-mat/0605137], the authors claim that they solved the linearized
Eilenberger equation in the ferromagnetic region of an S/F heterostructure at
arbitrary mean free path. In this comment we show that the solution suggested
by the authors is not correct and explain details of the exact solution found
by us in an earlier work several years ago (Phys. Rev. B 64, 134506, (2001).
