Many previous studies have shown that measurements of Pb isotopic compositions provide a powerful tool in determining the origin of Pb in a wide range of environments. In the present study, this method was applied to airborne particulate matter sampled in urban areas from two countries: France and the United Kingdom. Initially, the main potential sources of Pb contamination were defined isotopically. Three important end-members contribute to urban Pb load: the Pb added as an anti-knock agent in gasoline (defined by ²⁰⁶Pb/²⁰⁷Pb ≈ 1.061-1.094), industrially-derived Pb (²⁰⁶Pb/²⁰⁷Pb ratios ≈ 1.143-1.155) and « natural/local » Pb (derived from rocks and soils, ²⁰⁶Pb/²⁰⁷Pb ≈ 1.17-1.20). Urban airborne particulate matter, sampled only a few metres from dense car traffic, yields a wide range of ²⁰⁶Pb/²⁰⁷Pb values (1.085 - 1.158), which do not fall entirely within the gasoline domain. As a consequence of recent environmental legislation and increased use of unleaded gasoline, emission of car-derived Pb has been drastically reduced and today, other sources of Pb are important contributors to total Pb, even in urban environments. In addition, this study demonstrates that the contribution of each end-member can vary considerably over the short-term as a Junction of car traffic density and wind direction.