Current measurements of isospin splittings in mesons and baryons are sufficiently precise that they allow estimates of the mass difference between constituent up and down quarks. Some previous results are updated in the light of these new measurements, and the importance of better measurements of some observables such as $M(K^{∗±}), M(B^{∗0})-M(B^0)$, and isospin splittings in bottom baryons is noted.