In single-coated animal species selected for fibre production, such as sheep and Angora goats, nutrition is known to have a positive effect on fibre length and diameter, and hence on the weight of fibre produced, while in double-coated species, such as the cashmere goat, the fibre characteristics of the undercoat appear relatively insensitive to nutritional influence. Recent studies on the relationship between nutrition and fibre production in the llama, a double-coated species, indicate that it conforms to the above generalisation in that the growth rate and diameter of its fibre are not amenable to nutritional manipulation (Russel and Redden, 1994). There is a lack of information on the effects of nutrition on fibre characteristics and production in the other domesticated species of South American camelid, the single-coated alpaca. The experiment reported here was designed to provide such information.