The additive hydroxy-analogue of selenomethionine consists of synthetic R,S-2-hydroxy-4-methylselenobutanoic acid (HMSeBA) and is intended to be used as a source of the essential trace element selenium for all animal species/categories. Based on data from tolerance studies in chickens and turkeys for fattening and piglets, the additive is considered as safe for all species/categories up to the maximum authorised total selenium level in complete feed. After being absorbed, HMSeBA is metabolised to selenomethionine; consequently, no residues of the compound itself occur in animal tissues and products. Compared with inorganic selenium sources, the use of HMSeBA in animal nutrition would result in a similar increase in selenium deposition in animal tissues/products as that resulting from selenised yeast. To ensure consumer safety from consumption of food originating from animals supplemented with HMSeBA, the FEEDAP Panel concluded that selenium supplementation from the additive should not exceed a maximum of 0.2 mg Se/kg complete feed. The additive should be regarded as an eye irritant, but should not be classified as skin irritant or skin sensitiser. Inhalation exposure poses a hazard to users; the FEEDAP Panel concludes, therefore, that the formulation and conditions of use of the solid form of the additive should minimise user exposure by inhalation. The use of HMSeBA in feed does not pose an additional risk to the environment, compared to other sources of selenium for which it will substitute, as long as the maximum authorised content in feedingstuffs is not exceeded. Based on the response of plasma glutathione peroxidase activity and the plasma/liver concentration of selenium in chickens for fattening and pigs for fattening, the FEEDAP Panel considers that HMSeBA is an efficaceous source of selenium for all animal species/categories. HMSeBA does not modify the quality of meat as measured by physico-chemical properties.