We use the constraints arising from primordial nucleisynthesis to bound the strength F of non-standard neutrino-neutrino interactions, when the right-handed neutrinos participate in the interaction. We find F<3×10-3GF, which is five orders of magnitude more stringent than the limit obtained using LEP data. We also show that secret interactions of neutrinos mediated by massless particles must have a coupling f less than 2 × 10-5. This also ameliorates previous limits in the literature. © 1994.