This study is based on the measure of the 134 Cs and 13 7 Cs content in 298 samples belonging to 120 species of macromicetes, collected in 37 stations throughout the Friuli-Venezia Giulia Region (North Eastern Italy) in September-October 1986. Significant differences in contamination have been recorded both among species collected in the same station, and among average values of the stations themselves. The differences among species of the same stations seem to depend on the depth of the mycelium in the soil: contamination is highest in the fungi with superficial mycelium, lowest in those that are in symbiosis with deep-rooting deciduous trees. This is related to the fact that most of the radionuclides are presently concentrated in the upper horizon of the forest soil, as demonstrated by the analysis of 59 soil samples collected in the 37 stations. The differences among stations are well correlated to the amount of precipitation in the days following the Chernobyl disaster. This allowed the elaboration of a contamination map of the Friuli-Venezia Giulia Region based on precipitation and contamination data: the most polluted areas are located in the Carnian and Julian Pre-Alps, whereas the lowland has been but little affected by radioactive deposition. The average ratio 137 Cs/134 Cs in mushrooms is 2. 7, which is probably due to the presence in the materiai of 137 Cs deriving from nuclear tests.
