  A new method to constrain the cosmological equation of state is proposed by
using combined samples of gamma-ray bursts (GRBs) and supernovae (SNeIa). The
Chevallier-Polarski-Linder parameterization is adopted for the equation of
state in order to find out a realistic approach to achieve the
deceleration/acceleration transition phase of dark energy models. We find that
GRBs, calibrated by SNeIa, could be good distance indicators capable of
discriminating between cosmological models and $\Lambda$CDM model at high
redshift.
