To elucidate the dynamics of aluminium (Al),an element potentially toxic and strongly affected by acidifica-tion processes,in soils,we selected two regions that were similar in relief,soil types,and vegetation cover but differed markedly in their history of acid precipitation:the JizerskéMountains (anthropogenically acidified) and the Novohrad-ske Mountains (naturally acidified) in the Czech Republic.The levels of Al forms (exchangeable and organically bound)associated with different environmental impacts were meas-ured and univalent,divalent and trivalent Al species were quantified using HPLC/IC.Exchangeable and organically bound Al concentrations were higher in the anthropogeni-cally acidified area.Only the concentrations of the least-dangerous species,the univalent,in organic soil horizons were similar for both mountains.The concentrations of exchangeable Al forms were correlated with Ca concentra-tions and with pH in the organic horizon.The known rela-tionship of Al with soil pH was stronger in the mineral hori-zons.Relationships of exchangeable Al forms concentrations with sulphur concentrations or even more with the sulphur calcium molar ratio were found only in the Jizerské Moun-tains,not in the Novohradské.Generally,the obtained results support the hypothesis that mechanisms differed between natural and anthropogenic acidification.