The effects of dietary or parenteral administration of ascorbic acid on the adverse effects of excess tyrosine were investigated with young male White Leghorn chicks in a 2-week experiment. 2. Addition of 10 g ascorbic acid/kg to the control diet (without excess tyrosine) produced no beneficial effects on performance. Excess dietary tyrosine caused depressions in all measures of performance. 3. Adding 0.1, 1, 10 or 20 g ascorbic acid/kg to the diet containing excess tyrosine tended to improve performance. 4. Subcutaneous injection of 50 mg ascorbic acid/bird d to chicks receiving excess tyrosine brought about a significant improvement in body-weight gain. 5. The elevation of plasma free tyrosine caused by excess dietary tyrosine decreased as dietary ascorbic acid increased. 6. Ascorbic acid can alleviate, though not completely counteract, the adverse effect of excess dietary tyrosine.
