The Amitsur cohomology
groups H1(S∕R,Pic) and H2(S∕R,U) are computed in a number of cases where
R ⊆ S are rings of algebraic integers, with most specific results when R is Z and S is
the ring of integers in a quadratic nmher field. These results give information about
the Brauer group Br (S∕R), which gives a new proof of its vanishing when R = Z
and S is in an infinite class of quadratic extensions.