  Several works have now shown that nebular emission can have a significant
impact on broad-band photometry of high-redshift galaxies ($z > 3$), and how
this can affect parameter estimation from SED fitting. So far relatively small
spectroscopic samples have been used to measure this effect. Here we focus on a
large spectroscopic sample (N$\sim 2300$) at $z\sim2$, with measured H\alpha\
fluxes for $\sim100$ galaxies. Under appropriate assumptions, our SED fitting
code is able to reproduce observed H\alpha\ fluxes, and we infer that $\sim20$%
of our sample have parameters significantly affected when nebular emission is
taken into account. We also determine how nebular emission can affect selection
and parameter estimation of evolved galaxies (Balmer Break galaxies) at
high-redshift ($z\sim4$).
