  The Adler function D is found {\em exactly} in supersymmetric QCD. Our exact
formula relates D(Q^2) to the anomalous dimension of the matter superfields
\gamma (\alpha_s(Q^2)). En rout we prove another theorem: the absence of the
so-called singlet contribution to D. While such singlet contributions are
present in individual supergraphs, they cancel in the sum.
