Conventional K-Ar studies of volcanic rocks, rock-forming minerals and hydrothermal adularia and alunite from different volcanic centres of the Tokaj Mts indicate that volcanic activity took place between 15.2 and 9.4 Ma (Badenian-Sarmatian-Pannonian). In the northern part of the Tokaj Mts, ages for the relatively deeply eroded hydrothermal systems (Rudabanyacska and Telkibanya Au-Ag deposits and parts of the Regec caldera), formed mainly by the adularia-bearing low-sulphidation epithermal deposits, are between 13.0 and 12.2 Ma. These systems were developed within andesitic-dacitic volcanic centres with calderas and subvolcanic intrusions. In the southern parts of the Tokaj Mts (near Mad and in the Szerencs Hills region) exposures of hydrothermal systems mainly represent shallow acid-sulphate steam-heated zones of low-sulphidation-type systems, and the K-Ar ages are between 12.1 and 10.4 Ma. Radiometric ages also suggest that in some parts of this latter area, repeated hydrothermal activity occurred, suggesting that hydrothermal circulation developed in relation to different magmatic centres that were active at different times.