Antibiotics from within: antibacterials from human and animal sources.

The isolation of potent antibacterial proteins and peptides from human and animal phagocytes has raised the possibility that these 'antibiotics from within' can be used as therapeutic agents. Problems in delivery to and toxicity towards the host must be faced, but rapid progress in defining the structural determinants of the cytotoxic action of these naturally occurring cytotoxins provides a basis for biotechnological development of new classes of antibiotics.