Methionine is an essential amino acid in all animal species. Supplementation of appropriate amounts of methionine and analogues to meet requirements is safe for the target species. The use of methionine-based additives will not result in an increased content in tissues and products. Residues present in animal tissues and products resulting from the extremely small quantities of free styrene and 2-vinylpyridine found in DL-methionine copolymer (DL-Met-cop) are very unlikely to raise concerns about consumer safety. None of the products are considered to present a significant inhalation risk. DL-Methionine (DL-Met), DL-Met-cop and DL-methionine protected with ethylcellulose (DL-Met-ec) are non-irritant to skin and eyes, and the lack of sensitisation potential demonstrated for DL-Met is considered relevant to DL-Met-cop and DL-Met-ec. DL-Methionine sodium salt (DL-Met-Na) is considered to be corrosive to skin and eyes. The hydroxy analogue of methionine (HMTBa) is an irritant to the skin and corrosive to the eyes. The calcium salt of HMTBa, HMTBa-Ca, is irritant to the eyes. The absence of dermal sensitation potential demonstrated for HMTBa is considered relevant for HMTBa-Ca. The isopropyl ester of HMTBa, HMTB-i, is non-irritant to skin/eyes, and is not a dermal sensitiser. The use of these products as feed additives does not represent a risk to the environment. DL-Met, DL-Met-Na, HMTBa and HMTBa-Ca are effective dietary sources of methionine for protein synthesis in monogastric animals (including fish). The hydroxy analogues show a somewhat lower bioefficacy than the DL-methionine forms. They can all be used in ruminants, particularly when protected against ruminal degradation by specific formulations. DL-Met-cop, HMTB-i and DL-Met-ec escape ruminal degradation to a certain extent, the remainder being available for gastrointestinal absorption. The FEEDAP Panel does not support the use of the additives under application in water for drinking because of concerns about target animal safety and the maintenance of optimum performance.