  The perturbative $\beta$-function is known exactly in a number of
supersymmetric theories and in the 't Hooft renormalization scheme in the
$\phi_4^4$ model. It is shown how this allows one to compute the effective
action exactly for certain background field configurations and to relate bare
and renormalized couplings. The relationship between the MS and SUSY
subtraction schemes in $N = 1$ super Yang-Mills theory is discussed.
