Plasminogen (PG), urokinase‐type plasminogen activator (u‐PA) and tissue‐type PA (t‐PA) are the main molecules involved in fibrinolysis and in many other physiological and pathological processes. In the present study we report that human t‐PA, purified from human melanoma cells, and PG, purified from human plasma, both contain P‐Tyr residues, as revealed by immunoblotting analyses with monoclonal anti‐P‐Tyr antibodies. In addition HPLC amino acid analysis of acid‐hydrolyzed t‐PA, PG and u‐PA, shows that: (i)P‐Ser and P‐Tyr residues are present in t‐PA; (ii)P‐Thr and P‐Tyr are present in PG; (iii) P‐Ser, P‐Thr and P‐Tyr are present in u‐PA. The utilization of monoclonal anti‐P‐Ser and anti‐P‐Thr antibodies in immunoblotting experiments has confirmed these data which indicate that phosphorylation is a common feature of PAs and of PG.