Two experiments were conducted to study the post-prandial changes in protein synthesis rate of different tissues in juvenile Atlantic salmon after an i.v. injection of a large dose (1.5 pmole/g) of L- [ 2,3-3H] -1eucine. In the first experiment, the changes in protein synthesis rate of the muscle and scales were followed over a period of 18 h after a meal, in salmon (mean body weight 43.4 g) starved for 1 week. The rate of protein synthesis in muscle increased until 18 h after feeding. No significant changes were observed in the protein synthesis rate of the scales. In the second experiment, the salmon (mean body weight 36.8 g) were regularly fed on a commercial diet. Immediate analysis of protein metabolism (2 h after the morning meal) as compared with analysis after an overnight fast showed no significant effect of feeding on the protein synthesis rate in liver, gill, digestive tract and muscle.