  Recent experimental measurements of the Gottfried Sum Rule, and pp and pD
Drell-Yan processes, suggest significant violation of flavor symmetry in the
proton sea. This interpretation rests on the assumption of parton charge
symmetry. Our model calculations suggest charge symmetry violation [CSV] for
parton valence distributions of a few percent. Precision measurements of
structure functions in muon and neutrino experiments allow us to set rather
stringent experimental limits on CSV in certain kinematic regions. In another
region, these experiments suggest substantial CSV effects. We suggest
experiments which could test parton CSV.
