A classification of particles is suggested based on a Ũ (12) symmetry scheme. This is a relativistic generalization of the U (6) symmetry. The spin
1
2
and
3
2
baryons are each described by 20-component spinors which satisfy Bargmann-Wigner equations and belong to the 3̲6̲4̲ representation of the Ũ (12) group while the vector and p. s. mesons belong to the representation 1̲4̲3̲. The procedure for writing fully relativistic form factors is worked out in detail for baryon-meson and meson-meson cases. The new results are the following: (1)
F
C
(
q
2
)
F
M
(
q
2
)
∝
1
+
q
2
<
2
μ
>
m
, Where
F
c and
F
M are (Sachs) electromagnetic form factors. (2)
μ
D = 1 + 2 m /< μ >, where < μ > is the mean mass of the 1 - multiplet and m the nucleon mass. (3)
μ
ρ,K* = 3. The conventional U (6) results can be recovered by projecting to the positive energy subspace in the rest system for each particle. To any irreducible representation of the U (6) there corresponds one irreducible representation of Ũ (12) and vice versa.