  In the $2$-Machine Flow Shop problem with exact delays the operations of each
job are separated by a given time lag (delay). Leung et al. (2007) established
that the problem is strongly NP-hard when the delays may have at most two
different values. We present further results for this case: we prove that the
existence of $(1.25-\varepsilon)$-approximation implies P$=$NP and develop a
$2$-approximation algorithm.
