Measurements of the afterglow of the big bang suggest mysterious dark matter was about six times more abundant than ordinary matter in the early universe. That ratio should remain the same through time, but observations of all the stars, gas and dust in the nearby, modern universe can account for only about a quarter as much ordinary, or “baryonic”, matter as expected.
http://space.newscientist.com/article/dn11825-galaxy-collision-reveals-missing-matter.html