  We summarize our modelling of galaxy photometric evolution (GRASIL code). By
including the effects of dust grains and PAHs molecules in a two phases clumpy
medium, where clumps are associated to star forming regions, we reproduce the
observed UV to radio SEDs of galaxies with star formation rates from zero to
several hundreds $M_\odot/yr$. GRASIL is a powerful tool to investigate the
star formation, the initial mass function and the supernovae rate in nearby
starbursts and normal galaxies, as well as to predict the evolution of
luminosity functions of different types of galaxies at wavelengths covering six
decades. It may be interfaced with any device providing the star formation and
metallicity histories of a galaxy. As an application, we have investigated the
properties of early-type galaxies in the HDF, tracking the contribution of this
population to the cosmic star-formation history, which has a broad peak between
z=1.5 and 4. To explain the absence of objects at z $\gsim$ 1.3, we suggest a
sequence of dust-enshrouded merging-driven starbursts in the first few Gyrs of
galaxies lifetime. We are at present working on a complementary sample of late
type objects selected in a similar way.
