  A radio labeling is an assignment $c:V(G) \rightarrow \textbf{N}$ such that
every distinct pair of vertices $u,v$ satisfies the inequality
$d(u,v)+|c(u)-c(v)|\geq \diam(G)+1$. The span of a radio labeling is the
maximum value. The radio number of $G$, $rn(G)$, is the minimum span over all
radio labelings of $G$. Generalized prism graphs, denoted $Z_{n,s}$, $s \geq
1$, $n\geq s$, have vertex set $\{(i,j)\,|\, i=1,2 \text{and} j=1,...,n\}$ and
edge set $\{((i,j),(i,j \pm 1))\} \cup
\{((1,i),(2,i+\sigma))\,|\,\sigma=-\left\lfloor\frac{s-1}{2}\right\rfloor\,\ldots,0,\ldots,\left\lfloor\frac{s}{2}\right\rfloor\}$.
In this paper we determine the radio number of $Z_{n,s}$ for $s=1,2$ and $3$.
In the process we develop techniques that are likely to be of use in
determining radio numbers of other families of graphs.
