Different forms of selenium may have varying bioavailability and may also have different effects on body physiology. For these reasons we have studied the occurrence of different forms of selenium in some foods. The pattern of soluble selenium compounds in different species of fish varied markedly as studied by size-exclusion chromatography coupled to ICP-MS or GFAAS. Most flatfish contained mainly low-molecular-weight selenium compounds while other fish species contained more protein-bound selenium. Studies of muscle from seven meat animal species showed four major selenium peaks as found by size-exclusion chromatography. The second and third peaks probably corresponded to glutathione peroxidase (GPx) and selenoprotein W, respectively, and they contained 85% –100% of the recovered selenium. The distribution among the four peaks of soluble selenium varied considerably among muscles from different species. In other experiments, several factors were found to affect the activity of GPx in tissues such as species differences, tissue specificity and heating. In bovine milk, another selenium-rich food, GPx3 is the only identified selenoprotein so far. Bovine whey was found to contain most of the selenium in β-lactoglobulin, α-lactalbumin and selenomethionine. Supplementation of the cow’s feed by yeast selenium increased the proportion of selenium in the former two fractions. It can be concluded that different animal foods contain a variety of selenium compounds and that the selenium profiles of fish, meat and milk differ markedly and also show species differences. The role of this diversity for the bioavailability of selenium from different foods and the effects of different forms of selenium on the organism need to be explored.