  We discuss the uncertainties and the systematic effects that exist in the
estimates of the stellar masses of high redshift galaxies, using broad band
photometry, and how they affect the deduced galaxy stellar mass function. We
use at this purpose the latest version of the GOODS-MUSIC catalog. In
particular, we discuss the impact of different synthetic models, of the assumed
initial mass function and of the selection band. Using Charlot & Bruzual 2007
and Maraston 2005 models we find masses lower than those obtained from Bruzual
& Charlot 2003 models. In addition, we find a slight trend as a function of the
mass itself comparing these two mass determinations with that from Bruzual &
Charlot 2003 models. As consequence, the derived galaxy stellar mass functions
show diverse shapes, and their slope depends on the assumed models. Despite
these differences, the overall results and scenario remains unchanged. The
masses obtained with the assumption of the Chabrier initial mass function are
in average 0.24 dex lower than those from the Salpeter assumption, at all
redshifts, causing a shift of galaxy stellar mass function of the same amount.
Finally, using a 4.5 um-selected sample instead of a Ks-selected one, we add a
new population of highly absorbed, dusty galaxies at z\simeq 2-3 of relatively
low masses, yielding stronger constraints on the slope of the galaxy stellar
mass function at lower masses.
