Biocidal proteins isolated from seeds have been characterized, in particular proteins isolated from members of the Brassicaceae, Compositae and Leguminosae families including Raphanus, Brassica, Sinapis, Arabidopsis, Dahlia, Cnicus, Lathyrus and Clitoria. The proteins show a wide range of antifungal activity and some are active against Gram-positive bacteria. All share a common amino acid sequence. DNA encoding the proteins has been isolated and incorporated into vectors. Plants transformed with this DNA may be produced. The proteins find commercial application as antifungal or antibacterial agents; transformed plants will show increased disease-resistance.