The class of commutative dually residuated lattice ordered monoids (DRl-monoids) contains among others Abelian lattice ordered groups, algebras of Hajek's Basic fuzzy logic and Brouwerian algebras. In the paper, a unary operation of negation in bounded DRl-monoids is introduced, its properties are studied and the sets of regular and dense elements of DRl-monoids are described.