A collection of monoclonal antibodies was raised against bovine plasminogen by immunizing mice with purified plasminogen. More than 300 positive clones were obtained in 1 fusion experiment (1300 hybrids tested). Four types of antibodies were characterized through their relative binding to plasmin and plasminogen in ELISA. About one-third was strictly specific to plasminogen; the selectivity of this group was confirmed by immunoblots and BIA-core analysis. Cross-reactivity against horse, human, pig, sheep, rabbit, and bovine plasminogens was tested; 41% were strictly bovine specific.