Radiotracers were used to study processes controlling the accumulation and elimination of vanadium in the Mediterranean mussel Mytilus galloprovincialis. Vanadium uptake rates varied inversely with both salinity and vanadium concentration in water, but were independent of temperature. After a 3 wk exposure to 48V, the highest concentration factors were found in the byssus (≈1900) with much lower values computed for shell (≈ 70) and soft tissues (≈5). More than 90% of the total 48V accumulated was fixed to shell, suggesting that uptake is primarily a result of surface sorption processes. Much of the vanadium in shell was firmly bound to the periostracum and was not easily removed by acid leaching. Food-chain experiments indicated that the assimilation coefficient for ingested vanadium is low (≈7%) and that the assimilated fraction is rapidly excreted from the mussel. These findings coupled with knowledge of in situ and experimentally-derived vanadium concentration-factors have allowed a preliminary assessment of the relative importance of the food and water pathways in the contamination of mussels under conditions of acute and chronic exposure. Contaminated mussels transferred to clean sea water lost 48V at rates that depended upon temperature but were largely unaffected by either salinity or by vanadium levels in mussel tissues. Total vanadium depuration was slow and was governed by loss from a slowly-exchanging compartment with a characteristic half-time of about 100 d. Individual mussel tissues were analyzed for stable vanadium and the possibility of using these tissues, particularly the byssus, as bioindicators of ambient vanadium levels in the marine environment is also discussed.