The levels of 10 polynuclear aromatic hydrocarbons (PAHs), phenanthrene, fluorene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene and benzo[g,h,i]perylene, were determined in the leaves of the bay evergreen tree (Laurus nobilis) taken from 15 different sites in the Valley of Florence. The measurements were repeated for three different seasons (summer, autumn, winter). The concentration of all PAHs increased during the year with maximum levels occurring during the winter. The elemental analysis of the leaves (K, Si, P, S, Ca, Pb, Br, Mn, Fe, Sr, Zn, Cu) showed a good correlation between PAHs and lead or bromine levels, indicating that the main source of PAHs deposited on the leaves was vehicular traffic. The levels of PAHs on the leaves were also well correlated with air levels at two different sites