Of the characters used for stock differentiation in the North Sea herring, fecundity studies have proved confusing to the general picture of separation into three major stocks, Bank, Downs and Buchan. By combining fecundity counts with length, a fecundity index has resulted which clearly discriminates between Bank and Downs fish. The index has been used to separate these two stocks in the mixed North Shields fishery. The proportions determined by this method compared well with those derived from other methods. The Bank fecundity/length relationship obtained here is indistinguishable from that derived earlier by Baxter from the northwestern North Sea spawning fisheries. It is suggested that these fish were not representative of pure Buchan spawners and were probably mainly Bank herring with some Buchan spawning fish.