Pb isotope compositions were determined on sulfides collected from vent fields on the spreading ridge. On Pb-Pb diagrams, the compositions are within both the MORB field and the least radiogenic part of the NFB basalt domain. Compared with the rather large variation of Pb isotope composition of the NFB basalts, the data indicate a remarkable homogeneity of Pb isotope ratios in the hydrothermal sulfides studied, and suggest that sulfide lead reflects the average isotope composition of the upper part of the oceanic crust affected by hydrothermal processes. Thus, for the upper mantle below the NFB, sulfide lead indicates the presence of a DUPAL-type anomaly, or contamination by recently subducted sediments. The data also reveal isotopic heterogeneities at a ridge-segment scale that are correlated with petrological variations of NFB ridge basalts. There is an abridged English version.