Quasar absorption lines provide a unique tool to detect baryonic matter at all redshifts in a luminosity unbiased way. In this talk, I will present a survey for neutral gas at high redshift, detected along the line of sight to quasars form the Sloan Digital Sky Survey. These systems have long been thought to be the imprint of the interstellar gas of high-redshift galaxies. I will discuss the evolution of the cosmological mass density of neutral gas from z 4 to the present time. Then I will present new clues to search for the densest phases of the interstellar medium (closely related to star-forming regions) of high-z galaxies. Finally, I will present a direct search for emission-line from the associated galaxies.