  We present a construction kit for calculating two-loop beta functions in N=1
supersymmetric theories for the operators of the superpotential using
supergraph techniques. In particular, it allows to compute the beta functions
for every desired, even higher dimensional, operator of the superpotential from
the wavefunction renormalization constants of the theory. We apply this method
to calculate the two-loop beta functions for the lowest-dimensional effective
neutrino mass operator in the Minimal Supersymmetric Standard Model (MSSM) and
for the Yukawa couplings in the MSSM extended by singlet superfields and the
mass matrix for the latter. Our method can be applied to any N=1 supersymmetric
theory.
