The effect of administering triamcinolone acetonide (10 mg/kg/day), 6 consecutive s.c. injections given daily, on plasma free amino acids and urinary urea output was studied in rabbits. 2. The total free amino acids in plasma decreased significantly from day 2 while ammonia increased significantly only on day 2, glutamine, lysine and branched amino acids increased significantly from day 3 or 5. 3. The output of urinary urea increased significantly from day 3. 4. These findings suggest the inhibition of protein synthesis observed in steroid myopathy may result from a decrease in the amino acid pool in skeletal muscle.