Histidine-rich glycoprotein (HRGP), an abundant heparin-binding protein found in plasma and thrombocytes, exerts antibacterial effects against Gram-positive bacteria (Enterococcus faecalisand Staphylococcus aureus) and Gram-negative bacteria (Escherichia coliandPseudomonas aeruginosa). Fluorescence studies and electron microscopy to assess membrane permea-tion showed that HRGP induces lysis of E.