With the aid of inductively coupled plasma mass spectrometry (ICP-MS), (206/207)Pb isotope ratios were determined in 34 moss samples (Polytrichum formosum) taken from the Hoerner Bruch area near Osnabruck (FRG) in the years 1987-1996. The goal was to distinguish different sources of atmospheric lead pollution by the investigation of lead isotope ratios. Reproducibility tests were carried out to ensure the reliability of analyzing Pb isotope ratios in moss samples by means of quadrupole ICP-MS. The reproducibility of the isotope ratios for one digested sample and the day-to-day reproducibility were determined. In all the moss samples analyzed, relative standard deviations of <0.26% for five replicate measurements of one digested sample were achieved for the (206/207)Pb isotope ratios. On the basis of the (206/207)Pb isotope ratio, it was possible to establish that the sources of man-made atmospheric inputs of lead have changed over the 10-year period investigated. In the moss samples analyzed, the (206/207)Pb isotope ratio was found to have risen significantly from 1.131 in 1987 to 1.154 in 1996. This increase in the (206/207)Pb isotope ratio can be attributed to a reduction of atmospheric inputs of lead from petrol.