Ingestion expts. using gaseous samples, saliva, urine, blood, and feces were conducted to investigate human metab. of the metalloids selenium, mercury, arsenic, and bismuth. Some differences exist in the metab. of metalloids in the human body. Contrary to selenium, ingestion of arsenic and bismuth compds. increased the total amt. and speciation of these elements in urine and blood. Most of the ingested bismuth ends up in the colon, where hydride formation and methylation occurs, eventually leading to the presence of bismuthine and methylated bismuth species in blood and breath. The process of biol. element volatilization in the colon can also be demonstrated for antimony, and may be similar for mercury. In the latter case, highly neurotoxic methylated mercurials will be formed.