Proteinase activity in the midgut of the pentatomid stinkbug Podisus maculiventris was investigated. The optimal pH for adult and nymph proteolysis was pH 6.0 and pH 6.5, respectively. Proteinase activity was characterised using a range of diagnostic inhibitors. Activity of both adult and nymphal gut extracts, detected by the hydrolysis of Z-Phe-Arg-pNA, was inhibited to <20% of control levels by several inhibitors (e.g. E-64 and chicken egg white cystatin) associated with the inhibition of cysteine proteinases. The less specific inhibitor leupeptin reduced proteolytic activity to around 1.0% of the control values. In-gel analysis of the enzymes revealed that proteolytic activity was due to at least four proteinases, of ca. 30, 36, 50 and 110 kDa, which were all susceptible to E-64 inhibition. Salivary gland extracts gave maximal activity at pH 8.0 when tested for general proteolytic activity using fluorescent BODIPY-FL casein substrate, and showed moderate levels of inhibition when incubated with inhibitors of serine-, cysteine-, aspartic- and metallo-proteinases. Leupeptin and PMSF gave the highest levels of inhibition of salivary proteolytic activity, at ca. 50%, whilst the plant-derived inhibitors SKTI, CpTI and OC-1 did not inhibit proteolysis.