Moss-bags have been used earlier for absorbing atmospheric metal pollutants in England around local emission sources (Goodman & Roberts 1971, Goodman et al. 1974, Little & Martin 1974). This paper describes the first results on the use of this method in Finland. In addition to Sphagnum mosses, experiments have also been made with other materials, including weakly decomposed Sphagnum peat. The moss-bags were roughly spherical balls of ca. 7 cm diameter containing on average 3 g (dry weight) of Sphagnum moss (Fig. 1). The dimensions of the peat-bags were smaller (Fig. 5), but the weight was approximately the same. After the period of exposure (1 to 3 months according to metal load), the material was oven-dried (at +50°C), dry-ashed at +450°C and finally the ash was dissolved in concentrated HC1 on a hot plate. The metals were determined by atomic absorption spectrometry at the Botany Dept., University of Helsinki. Sphagnum girgensohnii was collected from southern Finland and S. fuscum from northern Finland where the background metal contents are low (cf. Pakarinen & Tolonen 1976). Peat was collected from a depth of 60—100 cm, i.e. below the higher concentrations in the surface layers (cf. Pakarinen & Tolonen 1977).Preliminary results concerning the use of different materials in the Helsinki city area are presented in Table 1 (for study site, see Fig. 2). It appears that Sphagnum species of the Acutifolia group (S. fuscum and S. girgensohnii), as well as weakly decomposed Sphagnum peat, are more efficient collectors of airborne heavy metals than other materials used in the experiment (such as peat pots or cotton-wool). The seasonal variability in the metal content of different materials in the urban study site in Helsinki can be seen in Figs. 3 and 4. In particular the values for lead, but also to some extent for copper and zinc, are smaller during summer months. A similar seasonality in Helsinki has been earlier found for lead, e.g., with chemical monitoring (Nordman 1975). Outside the city area moss- and peat-bags have been used to study local effects of factories and highways. During a month's period in the autumn, the moss-bags collected high quantities of Pb and Zn near a lead smelter in Tikkurila (Fig. 6). Similarly, along a highway transect the total absorption of lead by peat-bags decreased steeply with distance (Fig. 7). The remarkable feature in both cases was a very small variability in the replicate samples at each distance from the local source. Using Sphagnum material from northern Finland, an extensive net of moss-bag stations has been established across Finland to study the applicability of this method for large-scale regional mapping of the fallout of different heavy metals. (Fig. 8). The technical development of the moss-bag method will continue in 1978, but already the results obtained so far do suggest that moss- and peat-bags can be recommended as an economic and efficient monitoring method, particularly where the living plants (lichens or mosses, e.g.) are absent or rare. For the laboratory analyses I am grateful to Mrs. Sirkka Heikkinen. This study has been supported by a grant from the Maj and Tor Nessling's Foundation to the research group Tolonen — Mä-kinen — Pakarinen.