The possible role of arsenosugars as precursors to arsenobetaine was investigated by feeding pure arsenosugar compounds to the shrimp, Crangon crangon, and monitoring the arsenic metabolites in muscle, midgut gland, gills, and 'remainder' tissues by HPLC-ICP MS. Control shrimps contained arsenobetaine (ca 90% of the total As) as the major arsenic compound in all four tissues, and traces of tetramethylarsonium ion and two arsenosugars were also present. Shrimps accumulated only 0.9% of a dimethylated arsenosugar, mostly as unchanged compound, and conversion into arsenobetaine could not be detected. Dimethylarsinate and possibly dimethylarsinoylethanol were present as minor metabolites. Shrimps accumulated 4.2% of a trimethylated arsenosugar, and converted about half into arsenobetaine. The remainder of the arsenic was present as unchanged arsenosugar and several minor unidentified metabolites. The overall accumulation of arsenobetaine from ingested trimethylated arsenosugar was only about 2%, whereas shrimps fed arsenobetaine retained 57% of the dose. The undetectable (dimethylated) to low (trimethylated) conversion of the arsenosugars into arsenobetaine suggests that these compounds do not represent a major source of arsenobetaine for wild Crangon.