First results on the running coupling in QCD with two massless flavours

We report on the non-perturbative computation of the running coupling of tw o-flavour QCD in the Schrodinger functional scheme. The corresponding A-par ameter, which describes the coupling strength at high energy, is related to a low energy scale which still remains to be connected to a hadronic "expe rimentally" observable quantity. We find the non-perturbative evolution of the coupling important to eliminate a significant contribution to the total error in the estimated A-parameter. (C) 2001 Elsevier Science B.V. All rig hts reserved.