Extending our studies of the effect of arsenite on the metabolism of inorganic selenium (selenite and selenate) to lower doses, we intravenously injected New Zealand white rabbits with aqueous solutions of arsenite, selenite, arsenite + selenite, selenate and selenate + arsenite at 50 µg and 5 µg metalloid per kilogram body weight. Bile samples were collected for 25 min, acid-digested and analyzed for total arsenic and selenium by double focusing magnetic sector field inductively coupled plasma mass spectrometry. At both dose levels, and in accord with previous observations, an increased mutual biliary excretion of arsenic and selenium was observed regardless of whether selenium was coadministered with arsenite in the form of selenite or selenate. Based on our previous investigations into the in vivo interaction between arsenite and selenite (or selenate), these findings can be rationalized in terms of the biliary excretion of the seleno-bis(S-glutathionyl) arsinium ion, [(GS)2AsSe]−. In addition, the treatment of rabbits with 50 µg arsenic per kilogram body weight in form of arsenite alone also resulted in a significantly increased bile selenium concentration compared with bile from untreated animals (p < 0.05), which implies a mobilization of endogenous selenium to bile. Combined, these results establish a causal relationship between the exposure of mammals to arsenite and selenium deficiency.