Two models for a gauge theory of the weak and electromagnetic interactions of leptons and hadrons are considered. The first model is based on the group [SU(3)] 4 = SU(3) × SU(3) × SU(3) × SU(3), the fundamental representation of which is spanned by left and right-handed lepton and quark triplets. The lepton triplet involves the ν e and ν μ combined to a 4 component field, the e − and the μ +. A spontaneous symmetry breakdown is caused by the appearance of tadpoles. It is proved that the tadpoles responsible for the lepton and quark masses, by themselves, do not break the symmetry in a manner compatible with the observed universality properties of weak interactions. Many additional scalar fields are needed and they are classified into specific [SU(3)] 4 multiplets. The model can account for the suppression of | ΔS| = 1 neutral current induced semileptonic decays ( K → πν ν, K° → μ +μ − , etc…) A quartet model based on the symmetry U(4) × U(4) is discussed. The model is simpler, but has to confront the absence of “charmed” hadrons in the low ( m ⩽ 2−3 GeV) mass region.