The determination of the pregalactic helium mass-fraction is addressed. Previous attempts to empirically determine Yp from a constant parameter dY/dZ are critically discussed, and new results based on extensive spectroscopy of emission-line galaxies by Terlevich and Melnick (1981) are examined. It is concluded from these new results that helium may correlate better with nitrogen than with oxygen. If Y is plotted against N/H, a single relationship holds for all objects, all the relationships extrapolating back to Yp = 0.237 + or - 0.005. It is suggested that the large value of dY/dZ in blue compact galaxies and the (Y, N/H) relation are due to local contamination by winds from Wolf-Rayet stars.
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Pagel et al. (1986) studied this question.