The presence of methylated antimony species has been reported in surface waters, sediments, soils, and biota, mainly detected using hydride generation techniques. Compared to other elements, relatively few studies have been published. Monomethyl-, dimethyl-, and trimethylantimony species have been found, always at very low concentrations. It is important to point out that (i) it has been proved that the identity of some of the published species might be uncertain due to possible artefacts during the analytical process; (ii) existing analytical methods do not reveal the oxidation state of the antimony in the detected species. Volatile methylated species have also been detected in landfill and sewage fermentation gases. Laboratory culture experiments have indicated that biomethylation can result from bacterial, yeast, and fungal activity, in both aerobic and anaerobic conditions. Antimony is methylated much less rapidly and less extensively than arsenic and it has been suggested that antimony biomethylation could be a fortuitous rather than a detoxification process.