The advantages and drawbacks of membrane inlet mass spectrometry (MIMS) for identification of volatile selenium compounds were investigated. Hepatocytes were incubated with methylseleninic acid (MeSeA) directly in the MIMS reaction cell and dimethyl diselenide (DMeDSe) was identified as the major volatile metabolite. This compound was also identified as the major reaction product after incubation of glutathione (GSH) with MeSeA without the presence of hepatocytes. One advantage of MIMS is the possibility of in situ monitoring of volatile metabolites with minimum risk of sample loss and without the need for trapping devices. Another advantage is the possibility of concurrent monitoring of cell viability by simultaneous detection of oxygen consumption and CO2 production. Although ideal for screening, the technique suffers from a relative high detection limit (in the 1 µM range) and lack of robustness. This paper presents for the first time in situMS data on the formation of DMeDSe.