  We propose the "supersymmetric (SUSY) Yukawa sum rule", a relationship
between physical masses and mixing angles of the third-generation quarks and
squarks. The sum rule follows directly from a relation between quark and squark
couplings to the Higgs, enforced by SUSY. It is exactly this relation that
ensures the cancellation of the one-loop quadratic divergence in the Higgs mass
from the top sector. Testing the sum rule experimentally would thus provide a
powerful consistency check on SUSY as the solution to the gauge hierarchy
problem. While such a test will most likely have to await a future
next-generation lepton collider, the LHC experiments may be able to make
significant progress towards this goal. If some of the terms entering the sum
rule are measured at the LHC, the sum rule can be used (within SUSY framework)
to put interesting constraints on the other terms, such as the mixing angles
among third-generation squarks. We outline how the required mass measurements
could be performed, and estimate the accuracy that can be achieved at the LHC.
