[en] Big-bang nucleosynthesis has been calculated for a universe with nonzero and unequal electron and muon lepton numbers. A comparison of the observed abundances of ⁴He and D with the values obtained in the calculations shows that the introduction of nonzero lepton numbers allows a wide margin of mean mass-energy densities at the present epoch, 10^-31 g cm^-3approximately-less-thanrho₀approximately-less-than 10^-28 g cm^-3. Hence the deuterium abundance is not as sensitive a gauge of rho₀ as has been thought. The permissible ranges of all the quantum numbers of the Universe are discussed