The potential of GC-MS for structure anal. of organometal(loid) species of arsenic, tin, antimony and tellurium in environmental samples was studied. Analytes were ionic organometal(loid) species from compost samples, which were derivatized with NaBH4 before introduction into the GC/MS via a purge and trap system, as well as volatile species from hydrothermal gases sampled on SPME-fibers. Several org. species of arsenic, tin, antimony and tellurium were identified. By scanning the chromatogram for typical fragments of organoarsenic compds. seven arsenic species were identified. To the authors' knowledge three of them (diarsine, monomethyl diarsine and dimethylarsenomercaptane) were not reported in environmental samples so far. To further exclude artifacts being misinterpreted as volatile organometal(loid)s, measurements of volatile arsenic species naturally occurring in hydrothermal samples with SPME-GC-MS were performed. The detn. of dimethylarsenomercaptane in these samples confirms that this compd. which was also found after derivatization of ionic arsenic species is not an artifact. A strategy for the identification of unknown species whose structure cannot be elucidated by library comparison or with the help of isotopic patterns is presented. The necessity of pos. identification of unknown species and confirmation of known and assumed compds. for speciation anal. is highlighted and the applicability of quadrupole GC/MS for this purpose is stated.