  We compute the equivariant K-theory with integer coefficients of an
equivariantly formal isotropy action, subject to natural hypotheses which cover
the three major classes of known examples. The proof proceeds by constructing a
map of spectral sequences from Hodgkin's K\"unneth spectral sequence in
equivariant K-theory to that in Borel cohomology. A new characterization of
equivariant formality appears as a consequence of this construction, and we are
now able to show that weak equivariant formality in the sense of
Harada--Landweber is equivalent with integer coefficients to surjectivity of
the forgetful map under a standard hypothesis.
  The main structure theorem is formally similar to that for Borel equivariant
cohomology, which appears in the author's dissertation/dormant book project and
whose proof is finally made accessible in an appendix. The most generally
applicable corollary of the main theorem for rational coefficients depends on a
strengthening of the characterization of equivariant formality due to Shiga and
Takahashi, which appears as a second appendix.
