  The theory of link-homotopy, introduced by Milnor, is an important part of
the knot theory, with Milnor's mu-bar-invariants being the basic set of
link-homotopy invariants. Skein relations for knot and link invariants played a
crucial role in the recent developments of knot theory. However, while skein
relations for Alexander and Jones invariants are known for quite a while, a
similar treatment of Milnor's mu-bar-invariants was missing. We fill this gap
by deducing simple skein relations for link-homotopy mu-invariants of string
links.
