  The packing chromatic number $\chi$ $\rho$ (G) of an undirected (resp.
oriented) graph G is the smallest integer k such that its set of vertices V (G)
can be partitioned into k disjoint subsets V 1,..., V k, in such a way that
every two distinct vertices in V i are at distance (resp. directed distance)
greater than i in G for every i, 1 $\le$ i $\le$ k. The generalized theta graph
$\Theta$ {\ell} 1,...,{\ell}p consists in two end-vertices joined by p $\ge$ 2
internally vertex-disjoint paths with respective lengths 1 $\le$ {\ell} 1 $\le$
. . . $\le$ {\ell} p. We prove that the packing chromatic number of any
undirected generalized theta graph lies between 3 and max{5, n 3 + 2}, where n
3 = |{i / 1 $\le$ i $\le$ p, {\ell} i = 3}|, and that both these bounds are
tight. We then characterize undirected generalized theta graphs with packing
chromatic number k for every k $\ge$ 3. We also prove that the packing
chromatic number of any oriented generalized theta graph lies between 2 and 5
and that both these bounds are tight.
