To determine differential gene expression profiles in the salivary gland of a predatory flower bug species, Orius laevigatus Fieber, a subtractive cDNA library was constructed by suppression subtractive hybridization. Digestion-related genes, including trypsin, hemolysin, lipase, cathepsin, and peritrophin, occupied 35% of the EST library. The major transcripts encoded trypsin-like serine proteases (223 ESTs, 28.8% of the total ESTs). A hemolysin gene occupied ca. 8% (42 ESTs) of the library. Hemolysin in saliva may be cytotoxic against the prey cells, thereby allowing O. laevigatus to facilitate feeding. An anticoagulation factor, lumbrokinase, also appears to act as a feeding-facilitating factor. Carbonic anhydrase, glutation peroxidase, alkaline phosphatase, and glutation S-tranfterase are expected to function as antioxidants, pH regulation- or homeostasis-related reagents in the saliva. Bactericidal permeability-increasing protein and peritrophin might protect insects from microbial infection. Interestingly, a neuroendocrinein and a huntingtin-interacting protein that could disturb the neuronal system were found in the salivary gland-specific EST library.