  Superfluid $^{3}$He experiments show strong deviation from the weak-coupling
limit of the Ginzburg-Landau theory, and this discrepancy grows with increasing
pressure. Strong-coupling contributions to the quasiparticle interactions are
known to account for this effect and they are manifest in the five
$\beta$-coefficients of the fourth order Ginzburg-Landau free energy terms. The
Ginzburg-Landau free energy also has a coefficient $g_{z}$ to include magnetic
field coupling to the order parameter. From NMR susceptibility experiments, we
find the deviation of $g_{z}$ from its weak-coupling value to be negligible at
all pressures. New results for the pressure dependence of four different
combinations of $\beta$-coefficients, $\beta$_{345}, $\beta$_{12},
$\beta$_{245}, and $\beta$_{5} are calculated and comparison is made with
theory.
