Moss bags of the aquatic bryophyte Rhynchostegium riparioides (Hedw.) C.E.O. Jensen (¼ Platyhypnidium riparioides (Hedw.) Dixon) were transplanted into freshwaters of the Province of Belluno (NE Italy). This study was aimed at testing the bioaccumulation of trace elements in Pre-alpine Dolomitic streams, where this species does not grow naturally, and where analyses of water samples have never revealed trace element pollution. Mosses were collected after 13, 26 and 59 days of exposure. The concentrations of nine trace elements in the apical shoots were measured. Average concentrations reached in three control stations were adopted as background values, to calculate the contamination factor (CF). Transplants accumulated trace elements and discriminated between non-or scarcely contaminated waters (low CF) and polluted ones (high CF). Furthermore, two patterns of contamination were revealed by multivariate analysis: (I) metals (Cr, Cu, Ni) from galvanic industries, and (II) metals (Pb, Zn) from other industrial/domestic sources or mine sites.