Let the field K be an abelian
extension of the rational field Q. The Schur group of K, S(K), consists of those
classes in the Brauer group of K which contain an algebra isomorphic to a
simple component of a rational group algebra QG for some finite group
G.
Suppose that K has a cyclic extension of the form Q(ζ) where ζ is a primitive
n-th root of unity. In this paper we calculate the 2-part of S(K) where K contains
the fourth roots of unity.