  The problem of primordial nucleosynthesis of helium in brane cosmology is
studied using a semi-analytical method, where the Fermi-Dirac statistic is
ignored. This semi-analytical method agrees with a more complete numerical
calculation with a precision of order of 10% or better. The quadratic term for
the matter density is the only source considered in the modified Einstein
equations predicted by the brane configuration. This hypothesis is justified a
posteriori. An agreement between theoretical and observational values for the
helium abundance is obtained if the fundamental mass scale in five dimensions
is of the order of $M \sim 5\times10^3 GeV$.
