  We have derived a primordial helium abundance of Yp = 0.2477 +- 0.0029, based
on new atomic physics computations of the recombination coefficients of He I
and of the collisional excitation of the H I Balmer lines together with
observations and photoionization models of metal-poor extragalactic H II
regions. The new atomic data increase our previous determination of Yp by
0.0086, a very significant amount. By combining our Yp result with the
predictions made by the standard Big Bang nucleosynthesis model, we find a
baryon-to-photon ratio, \eta, in excellent agreement both with the \eta value
derived by the primordial deuterium abundance value observed in damped
Lyman-\alpha systems and with the one obtained from the WMAP observations.
