  We study the H$\alpha$ emission from jets using two-dimensional
axisymmetrical simulations. We compare the emission obtained from hydrodynamic
(HD) simulations with that obtained from magnetohydrodynamics (MHD)
simulations. The magnetic field is supposed to be present in the jet only, and
with a toroidal configuration. The simulations have time-dependent ejection
velocities and different intensities for the initial magnetic field. The
results show an increase in the H$\alpha$ emission along the jet for the
magnetized cases with respect to the HD case. The increase in the emission is
due to a better collimation of the jet in the MHD case, and to a small increase
in the shock velocity. These results could have important implications for the
interpretation of the observations of jets from young stellar objects.
