It has been shown by Beever, Thomson, Cammell and Harrison (1977) that formaldehyde treatment of silage increased amino acid absorption from the small intestine of sheep by 13% and increased the amount of food protein passing through the rumen undegraded by 66% compared to sheep receiving untreated silage. This paper details the digestion of N and apparent uptake of N, non-ammonia N and amino acid N from the small intestine of Jersey cattle fed a silage made from a second growth, mixed S24 perennial ryegrass/red clover sward which was wilted for 24h and then ensiled either without an additive or with a 50/50 mixture of formic acid and formaldehyde (formalin), each at the rate of 2.2 litres/tonne of grass ensiled. The method of ensiling was by use of an Eberhardt Silopresse (Benedict Agricultural Ltd., London). Each of the three cows fed each diet was equipped with a rumen fistula and re-entrant cannulae into the proximal duodenum and terminal ileum.