Abstract: Peptide-based compounds containing four invariant cysteine residues which have been optionally oxidized to contain two intramolecular disulfide bonds, or modified forms where the cysteines are replaced, are useful as preservatives and in preventing, treating, or ameliorating viral or microbial infection in animals and plants, and in inactivating endotoxin. These compounds, in one embodiment, are of the formula:A.sub.1 -A.sub.2 -A.sub.3 -A.sub.4 -A.sub.5 -C-A.sub.7 -C-A.sub.9 -A.sub.10 -A.sub.11 -A.sub.12 -C-A.sub.14 -C-A.sub.16 -(A.sub.17 -A.sub.18)(1)(SEQ ID NO:1)and the N-terminal acylated and/or C-terminal amidated or esterified forms thereof, either in optionally --SH stabilized linear or in cystine-bridged formwherein A.sub.1, A.sub.9, A.sub.10, and A.sub.11 are basic amino acids;A.sub.2 and A.sub.3 are small amino acids;A.sub.5, A.sub.7, A.sub.12, A.sub.14 and A.sub.16 are hydrophobic amino acids; andA.sub.4 is a basic or a small amino acid;A.sub.