In the context of large financial markets we formulate the notion of "no asymptotic free lunch with vanishing risk"(NAFLVR),under which we can prove a version of the fundamental theorem of asset pricing in markets with an(even uncountably)infinite number of assets,as it is for instance the case in bond markets.(NAFLVR)turns out to be an economically meaningful "no arbitrage" condition and is equivalent to the existence of a separating measure.