  A characterization of right (left) quasi-duo skew polynomial rings of
endomorphism type and skew Laurent polynomial rings are given. In particular,
it is shown that (1) the polynomial ring R[x] is right quasi-duo iff R[x] is
commutative modulo its Jacobson radical iff R[x] is left quasi-duo, (2) the
skew Laurent polynomial ring is right quasi-duo iff it is left quasi-duo. These
extend some known results concerning a description of quasi-duo polynomial
rings and give a partial answer to the question posed by Lam and Dugas whether
right quasi-duo rings are left quasi-duo.
