Clenbuterol, a β adrenergic agonist has been shown to increase nitrogen retention and decrease lipid deposition in cattle, sheep, pigs, poultry and laboratory rodents. Effects on nitrogen retention occur primarily in skeletal muscle (Williams et al 1987) and results suggest that reduced protein degradation is mainly responsible for the increased N retention. Reductions in N excretion were insufficient to account for the increased N retention in muscle and we demonstrated (Williams et al 1987) that increased N retention in skeletal muscle was occurring partly as a result of a nitrogen repartitioning in the body with reduced N retention in the viscera. Growth hormone also stimulates skeletal and muscle growth furthermore the mechanism whereby growth hormone stimulates N retention was considered to act primarily via a stimulation of protein synthesis (Eismann et al 1986). It would therefore appear that clenbuterol and growth hormone both increase N retention but by different mechanisms leading to the possibility of achieving an additive effect from the use of the two compounds in combination. The present experiment was designed to study the effects of clenbuterol and growth hormone individually and in combination on the N balance, creatinine excretion, protein and lipid accretion of veal calves.