Conventional protease activity assays, with the azocasein, casein and hemoglobin substrates, seem to be inappropriate for the determination of bug protease activity in wheat samples damaged by them bug (Eurygaster spp.). Electrophoresis results revealed that gluten is the best substrate for the bug protease. The enzyme also had some activity on gelatin. Two spectrophotometric methods, based on the solubility of gluten proteins in SDS solution and of glutenin in 50% 1-propanol, were developed for the determination of bug protease activity in bug-damaged wheat. On the other hand, it was found that the level of certain amino acids increased substantially with the action of bug protease. The greatest increases were observed in the contents of phenylalanine, proline, tyrosine and leucine. Overall results suggested that wheat bug protease has great substrate specificity for gluten proteins.