  An integer distance digraph is the Cayley graph $\Gamma(\mathbb{Z},S)$ of the
additive group $\mathbb{Z}$ of all integers with respect to some finite subset
$S \subseteq \mathbb{Z}$. The domination ratio of $\Gamma(\mathbb{Z},S)$ is the
minimum density of a dominating set in $\Gamma(\mathbb{Z},S)$. We establish
some basic results on the domination ratio of $\Gamma(\mathbb{Z},S)$ and
precisely determine it when $S=\{s,t\}$ with $s$ dividing $t$.
