We derived the primordial helium abundance in the Universe using spectral observations of low-metallicity blue compact dwarf galaxies. The intensities of hydrogen and helium emission lines were corrected for the stellar absorption and collisional excitation with the use of the Monte-Carlo simulations. As a result the best determined primordial helium abundance equals 0.2557±0.0014, 3 % higher than that derived from the analysis of fluctuations of the microwave background radiation assuming standard model of nucleosynthesis. This implies that new types of light neutrino species were present at the epoch of the primordial nucleosynthesis in addition to three known ones.