We have performed simulations of relativistic pressure-matched slab je
ts with beam Lorentz factors in the range 4.1 to 22.4 using a modem hi
gh-resolution shock-capturing technique based on an approximate relati
vistic Riemann solver. Our results show that the basic structural comp
onents found in Newtonian simulations, i.e. beam, cocoon, working surf
ace and bow shock, are also present in relativistic jets. We further f
ind that the head of the jet propagates at relativistic speed which de
pends on the beam velocity in a very non-linear way, and that relativi
stic jets seem to be more stable than Newtonian ones. Finally, our pre
liminary results strongly support the necessity of a more detailed stu
dy of the morphology and dynamics of relativistic jets.