The use of Pt and Rh as active components in automobile catalytic converters has led to increasing concentrations of these elements in several natural matrices. Because of this, the suitability of the use of a terrestrial moss (Pleurozium schreberi) for the passive biomonitoring of traffic-related Pt and Rh deposition was studied. The moss samples collected from Finland in and around areas with heavy traffic had increased Pt and Rh concentrations, with maximum values of 12.2 and 4.5 ng g(-1), respectively. In addition, the concentrations of commonly used catalytic converter additives (Al, Ce, La, Y, and Zr) and some elements related to traffic or mineral dust (Cd, Cu, Fe, Hf, Pb, and Zn) were also measured to obtain more information about the sources of Pt and Rh. Multivariate principal component analysis and cluster analysis were applied for identification of the emission sources of the elements. The results indicated a common traffic-related source of Pt and Rh. However, the results also showed that Pt and Rh concentrations in mosses are increased only in areas located close to traffic lanes.