Environmental studies using bryophytes (mosses) for biomonitoring of changes in atmospheric deposition of heavy metals in Slovakia started in 1990. The basic grid of monitoring sites was arranged according to a national forest monitoring program (ICP Forest Slovakia) in a 16x16 kilometer grid. Since than, within the monitoring program of the ICP Vegetation concentrations of toxic heavy metals As, Cd, Hg, Pb were monitored. Comparing the median values from 1990 and 1995 for Hg and 2000 for As with the median values from 2020, the concentration of metals in moss samples has a decreasing trend in the order Pb (89.87%) > Cd (86.32%) > Hg (70.80%) > As (38.17%). This study aims to evaluate the long-term trends in atmospheric toxic heavy metals deposition and quantify the reduction in metal concentrations from 1990 to 2020.