  The significant excess of events recently found by the H1 and ZEUS
Collaborations at HERA in the deep-inelastic e^+ p scattering for high
momentum-transfers squared Q^2>15000 GeV^2 over the expectation of the standard
model can be explained by either one of the following possible consequences of
the substructure of quarks and leptons: 1) production of leptoquarks (Phi), 2)
exchange of an excited Z boson (Z'), 3) intrinsic form factors of quarks (or
leptons), 4) intrinsic anomalous magnetic moments of quarks, 5) production of
excited quarks (q^*), and 6) that of excited positrons (e^*+). The masses of
these new particles are estimated to be m(Phi) = 280-440 GeV, m(Z') = 210-250
GeV, m(q^*) = 120-140 GeV, and m(e^*+) = 300-370 GeV, although the
possibilities 2) and 5) are excluded by the currently available experimental
constraints.
