The concentrations of lead in the femura (Pb-F) and the 5-aminolaevulinic-acid-dehydratase in blood (ALA-D) have been determined in three pigeon populations (50 birds each), caught at urban sites with different traffic densities. The following mean concentrations were found (Pb-F [mg/kg wet wt.]/ALA-D [U/I]): 10.7/18.8 in the low burdened group, 27.9/10.8 in the moderate burdened group, and 49.5/5.6 in the high burdened group. These values were compared with a controlled group of 50 farm pigeons from two remote pigeonries, sited well away from motorways (Pb-F: 1.0/ALA-D: 35.6). The result was a strong positive correlation of the Pb-F and an inverse correlation of the ALA-D to the number of cars per day at the different sites. These local effects contributed much more to the differences of the Pb-F and ALA-D (in comparison with the rural pigeons) than the over-all elevated lead background level in the city. It has been concluded that the pigeon is an almost ideal animal for monitoring a narrow range of environmental lead burden. The main reason for this is that this species is exceptionally stationary; the usual ranges of the feeding, nesting, and sleeping sites of the pigeon are not greater than several hundred meters.