Samples of Hylocomium splendens collected in 1977, 1985, and 1990 from the same sites in remote areas of Norway have been analyzed for a range of polychlorinated biphenyl (PCB) congeners. The ∑PCB concentration (sum of the concentration of the 37 congeners screened) declined in all samples from all locations. It is probable that this decline reflects the reduction in the global use and manufacture of these compounds. Because the samples had been air-dried prior to storage, the possibility of contamination due to contact with laboratory air was investigated. It was concluded that, while some contamination may have occurred, it was largely by the tri- and tetrachlorinated groups. General trends in the moss ∑PCB composition are therefore believed to reflect broad ambient changes in the PCB concentration over time. While ∑PCB concentrations have declined, temporal changes in the congener pattern in the samples collected from the same locations were noted. For example, in the south of Norway the relative concentrations of hexa- and heptachlorinated homologue groups decreased to a greater extent than they did in the north. This observation can be interpreted as evidence for differences in congener recycling through the environment according to their volatility, and it is tentatively suggested that this may provide evidence in support of the global fractionation hypothesis.