R .A . L I NC OL N AN D J . A. LE I GH . 1998. The binding of plasmin to Streptococcus uberis strain 0140 J was optimal in the pH range 5·0-5·5. Plasmin binding decreased exponentially with increasing NaCl concentration (0-0·8 mol l −1 ), reaching a minimum at NaCl concentrations exceeding 0·55 mol l −1 . Neither K ¦ , Mg 2¦ nor the metal chelator EDTA had any effect on the interaction. Plasmin binding was prevented, in a concentration-dependent manner, by the amino acids lysine, arginine and o-aminocaproic acid. Bound plasmin was also eluted from the bacterial cell using the same amino acids. Bound plasmin was lost from the bacterium in a time-and temperature-dependent fashion, the rate of plasmin loss increased with increasing temperature over the range 4-55°C, and the elution of plasmin from live and heat-killed bacteria was similar. Cell-bound plasmin was only partially inhibited by the physiological inhibitor a 2 -antiplasmin whereas the serine protease inhibitor aprotinin, and the active site titrant p-nitrophenyl-p-guanidiniobenzoate, inhibited the activity of the cell-bound plasmin by more than 95%.