Abstract
New measurements of λ6678 in the H II galaxies Tololo 1214-277, Michigan 461 and Tololo 0633-415, using the Anglo-Australian Telescope and a CCD detector, give helium abundances in close agreement with those derivable from the 4471 and 5876 lines previously observed by Terlevich. Furthermore, the exciting stars for the low-abundance objects T 1214-277 and Michigan 461 are so hot, and [O II] is so weak, that one can be quite sure independently of photo-ionization models that the correction for neutral helium is below 5 per cent. This strengthens previous estimates of a pregalactic helium abundance close to 0.230. Implications for particle physics and cosmology are briefly discussed.
