This study determined the effect of milk or carbohydrate-electrolyte supplementation immediately after resistance exercise on muscle protein breakdown before and after a 10-week resistance training program. Nineteen untrained males, 18-25 years of age, consumed either a carbohydrate-electrolyte (CHO) or milk (MILK) beverage immediately after a strenuous leg resistance exercise bout, both before and after training. Muscle protein breakdown, as estimated by 3-methylhistidine-to-creatinine ratio, was significantly reduced after resistance exercise for both groups, as the ratio was decreased by 19.9% from baseline on the day of resistance exercise. A trend was present for a training effect for 3-methylhistidine-to-creatinine ratio (p<0.07), as the reduction from before to after resistance exercise was greater after training. There was no difference in muscle protein breakdown between the groups. One hour after exercise, serum concentrations of amino acids were significantly elevated for MILK and significantly reduced for CHO. Serum glucose was significantly higher for both groups 30 minutes post-exercise than baseline, and serum insulin was greater than baseline 30 minutes and 1 hour after exercise. Serum insulin was significantly greater for CHO than MILK 1 hour after resistance exercise. No effect of training was observed for the response of serum amino acids, glucose, or insulin to resistance exercise with beverage ingestion. In conclusion, although the type of beverage ingested post-exercise affected serum insulin and amino acid concentrations, it did not influence the reduction in muscle protein breakdown observed after resistance exercise. A trend was present for a greater reduction in protein breakdown after training.