The results from a number of studies are presented which investigated responses in fibre production of British Cashmere and Angora goats to variation in protein and sulphur amino acid nutrition. Requirements for amino acids were considered in the context of the concentration of amino acids, including cysteine and methionine, in rumen microbial protein and in dietary protein supplements compared with the amino acid composition of hair fibre. Increases in fibre yield and diameter were consistently observed in Angora goats given good quality protein supplements or rumen protected intestinally available methionine (SmartamineTM M, Rhone-Poulenc). Cashmere yield was not influenced by protein supplementation but by methonine supplementation in one study, possibly reflecting the smaller quantitative synthesis of this fibre compared with mohair production.