Volatile metal(loid)org. species of geogenic and anthropogenic origin are analyzed by low temp. gas chromatog. coupled online with plasma mass spectrometry (LTGC/ICP-MS) with detection limits in the higher pg-range (per m3 gas). In respect to the detn. of aq. samples, this instrumental technique is combined with sample derivatization by the hydride generation technique. Volatile species of As, Sb, Se and I could be detected in gases over hot springs in British Columbia (Canada). Methylated species of Hg, Ge, As, Sb and Te were also detd. in concns. in the ng/kg- to low mg/kg-range in geothermal waters from Ruapehu, Waimangu, Waiotapu and Tokaanu (North Island, New Zealand); up to 1% of the total dissolved metal(loid)s are found in methylated forms. Volatile metal(loid)org. species of geogenic origin are compared with those emanating from anthropogenic sources (waste and sewage gases, river and harbor sediments). Possible formation mechanisms for these compds. are discussed.