  Various searches for leptoquarks, scalar quarks in $R_p$-violating
supersymmetric models, and excited fermions performed by the HERA experiments
H1 and ZEUS are reviewed. No evidence for new particle production was observed
from data collected by both experiments since 1994 in either electron-proton
and positron-proton collisions. Stringent limits derived on the masses and
couplings of these new particles are compared whenever appropriate with those
from LEP, the Tevatron and low energy experiments.
