Culture filtrate from Streptococcus uberis was found to activate bovine and equine plasminogen but not that from rabbit, human or porcine plasma. In contrast, streptokinase from a Lancefield group C Streptococcus activated human plasminogen but not that from bovine, porcine and rabbit plasma. Very slight activity was observed against equine plasminogen. Plasmin was detected by hydrolysis of skimmed milk protein in agarose. The activation of bovine plasminogen by S. uberis culture filtrate resulted in the formation of three polypeptides with molecular masses of 56, 26 and 21 kDa. This is the first report of a streptokinase activity from this species.