Abstract—After mice had been treated with L‐tyrosine,O‐phospho‐L‐tyrosine, L‐tyrosine methyl ester orN‐acetyl‐L‐tyrosine, tyrosine was assayed by HPLC coupled with fluorometric detection.O‐Phospho‐L‐tyrosine behaved as a tyrosine prodrug after its hydrolysis by acid and alkaline phosphatases. After the intraperitoneal administration ofO‐phospho‐L‐tyrosine or the methyl ester, there was a substantial increase in bioavailability in terms of the effect of tyrosine. The two prodrugs were as powerful as tyrosine following oral administration.N‐Acetyl‐L‐tyrosine was the least effective prodrug tested. The stability, solubility and bioavailability ofO‐phospho‐L‐tyrosine are consistent with proposing it for use as a tyrosine prodrug. In addition, it can be used parenterally. The use of a tyrosine aminotransferase inhibitor is necessary for limiting the hepatic breakdown of tyrosi