  We discuss mechanisms that change the hadron chemistry for high momentum
particles emitted in high energy nuclear collisions. We argue that particle
ratios naturally tend to be different from jets in the vacuum. We show results
of computations in a model that propagates leading particles through a quark
gluon plasma and permits elastic flavor changing processes. We predict less
suppression for kaons compared to pions in central collision. We also discuss
elliptic flow resulting from flavor changing processes.
