In the northwestern Mediterranean basin, lead concentrations in the surface waters have halved over the last 10 years. This decrease followed successive limitations of the use of lead additives in gasoline occurred in European countries since 1976 and the progressive use of unleaded fuel. The evolution of lead concentration in the Mediterranean waters is simulated by using a geochemical six-box model and validated by measurements made since 1983. In this way, it is demonstrated that: i) previous major pollution was essentially lead gasoline derived: ii) international antipollution policy is efficient; iii) the Mediterranean Sea is an important case study area to assess the marine biosphere's response to environmental changes. ¿ American Geophysical Union 1994