Allantoin has been detected in several plant families but only few papers reported its presence in lichens. The 18 from 21 lichen species we tested contained detectable amount of allantoin with a range of 0.005–13.4 mg/g DW. Comparison of samples collected from the localities with various intensity of “anthropopressure” (forest versus city) revealed that higher content of heavy metals was significantly correlated with elevated allantoin content mainly for Zn, Cu, and Ni (and in 3 from 5 species also for Cd and Fe). Subsequent laboratory experiments with four species showed that the accumulation of allantoin is rather stimulated by Cd, Pb or Ni in individual species but Hg had strongly negative impact. On the contrary, salinity had no impact in any species while simulated acid rain (pH 3) evoked various responses in four tested species. Data indicate that accumulation of allantoin depends on the eventual pollution of the given locality and metals have considerable impact on its content while the effect of individual stresses is rather specific.