The additive formaldehyde is an aqueous solution containing 35 % formaldehyde and 14 % methanol. It is intended for use in all animal species at concentrations between 200 and 1000 mg active substance/kg complete feed. Free and reversibly bound formaldehyde is readily absorbed in the gastrointestinal tract and joins the pool of endogenous formaldehyde. It is rapidly oxidised to formic acid further on to carbon dioxide and water. Formaldehyde is a carcinogen by inhalation. While local irritation is expected to strongly promote carcinogenesis, lower local concentrations of formaldehyde are known to produce DNA adducts. Therefore, the FEEDAP Panel deems it prudent not to consider the exposure to non-irritant concentration as totally riskless. Moreover, on the basis of the present knowledge, a causal association between formaldehyde exposure and leukaemia cannot be ruled out. The FEEDAP Panel estimated the oral intake of formaldehyde of consumers from food of animal origin to be 4 mg per person per day. A reliable additional exposure of consumers to formaldehyde from supplementing feedingstuffs cannot be calculated. However, the FEEDAP Panel considers that the proposed use of formaldehyde as a feed additive would not increase consumer exposure and consequently would not pose an additional risk for the consumer. A safe feed concentration for all animal species and categories could not be determined. Formaldehyde is a strong irritant, a potent skin and respiratory sensitiser. Measures should be taken to ensure that the respiratory tract, skin and eyes of any person handling the product are not exposed to any dust, mist or vapour generated by the use of formaldehyde. The use of formaldehyde in animal nutrition is not expected to pose a risk for the environment. Formaldehyde in concentrations between 200 and 1000 mg/kg feed (compound feed and/or feed material) has the potential to be an efficacious preservative.