Big-bang nucleosynthesis and the quark-hadron phase transition

The present status of our knowledge of the quark-hadron phase transition is reviewed. The uncertainties are assessed, in connection, mostly, with their relevance for primordial nucleosynthesis. The most important cosmological implication of these uncertainties is the following: The range of baryonic density compatible with the observations of the light nuclides is somewhat larger than estimated previously. This result, in turn, influences the status of the questions of the hypothetical existence of (1) baryonic dark matter, and (2) non-baryonic matter. I will point out a number of crucial weak points, in need of improvement. (orig.)