Most of the sharp absorption lines in the spectra of quasars of high red-shift are single Lyman-$\alpha $ lines. The stronger ones have associated Lyman-$\beta $ or Lyman-$\gamma $ lines but not lines of heavy elements. Recent statistical studies have shown that the density of Lyman-$\alpha $ absorption lines is statistically the same in all quasars and that the lines are randomly distributed, with no tendency to cluster. It is now thought that the single Lyman-$\alpha $ absorption lines are produced by primordial, intergalactic clouds. Studies now in progress are aimed at giving limits on the heavy-element composition of the clouds, as well as a value for the deuterium abundance of primordial gas.