[en] General properties of the SO(n) groups are examined, with emphasis on the usefulness of the Gel'fand-Zetlin basis for explicit calculations. The SO(n) representations containing a vector stabilized by subgroups of the type S[O(n - p) x O(p)], SU(k) x U(1) or SU(k) if n = 2 k, are characterized in view of selecting Higgs representations in SO(n) gauge models. Some useful properties of the SU(n) Gel'fand-Zetlin basis are given in the appendices. (orig.)