Methylation of metal(loid)s by bacteria or even mammals is a well known process that can lead to increased toxicity for humans. Nevertheless, reliable analytical techniques and tools are indispensable in speciation analysis of trace elements, especially since environmental or biological samples are usually characterised by complex matrices. Here the methylating capability of hepatic cells was observed in vitro. HepG2 cells were incubated with colloidal bismuth subcitrate, bismuth cysteine and bismuth glutathione, respectively for a period of 24 h. For identification the cell lysate was ethylated by sodium tetraethyl borate under neutral conditions. After cryo focussing by purge and trap, the bismuth speciation was carried out via GC/EI-MS/ICP-MS. Colloidal bismuth subcitrate and bismuth cysteine were methylated by HepG2 cells, while no methylated bismuth species was detected after incubation with bismuth glutathione.