The total concentration of mercury was determined in 15 species of wild growing mushrooms, each represented by 15 specimens including underlying substrate, collected from the unpolluted area of the sand-bar Mierzeja Wiślana in the northern part of Poland in 1993-1994. Mercury was measured by cold vapour atomic absorption spectrometry (CV-AAS) after wet digestion of the samples with concentrated nitric acid in a glass system. The mushroom species examined showed a wide range of mercury concentrations, i.e. from 5.6 +/- 2.1 micrograms/g dry wt. in Scleroderma citrinum to 1100 +/- 240 micrograms/g in the edible Macrolepiota procera. No bioconcentration of mercury was observed in Xerocomus badius, Paxilus involutus, Russula queletii and Lactarius rufus. In Hygrophorius aurantiaca, Armilariella mellea and Amanita vaginata the bioconcentration factor (BCF) values of mercury were close to one. Accumulation of mercury was slight in Oudemansiella platyphylla and Amanita citrica (BCF between 2.0 and 3.3 in the caps and 1.7 in the stalks) and high in Leccinum scabrurm, Amanita muscaria and Macrolepiota procera (BCFs between 11 and 35 in the caps and 6.7-18 in the stalks). In the whole fruiting body of Polyporus melanopsuss and Scleroderma citrinum the BCF values of mercury were 4.4 and 0.083, respectively. There was a high correlation between the concentrations of mercury in the caps and stalks of Macrolepiota procera and in the underlying substrate (P < 0.001), a slight correlation for Polyporus melanopsuss, and also for the caps of Leccinum scabrum, Oudemansiella platyphylla and Russula aeruginea and the stalks of Hygrophoropsis aurantiaca (P < 0.01) and L. scabrum (P < 0.05). For the other mushroom species investigated there was no correlation between mercury concentration in the fruiting bodies and underlying substrate.