  We discuss properties of the electroweak vacuum as a function of an external
magnetic field. The interest in these properties arises due to possible
existence of the electromagnetically superconducting phase of QCD in the
background of a sufficiently strong magnetic field. In the electroweak theory,
a superconducting vacuum exists for a well defined range of magnetic background
fields, and the interest of the current paper is the behaviour near the upper
critical magnetic field. We determine this critical field and calculate the
vacuum condensates to leading order.
