No single characteristic of virulent avian Escherichia coli has been identified that can be exploited in colibacillosis detection protocols. Research in our lab suggests a strong association between the presence of an iss DNA sequence with an isolate's disease-causing ability. The study presented here focuses on the techniques used in the expression, purification, and characterization of avian E. coli Iss protein. In brief, iss was cloned into an expression vector, the construct was transformed into a protease-deficient E. coli, and expression was induced. The protein was expressed as a glutathione-S-transferase (GST) fusion and purified by affinity chromatography. The GST portion was cleaved from Iss, Iss was harvested by affinity chromatography, and the identity of Iss was confirmed by N-terminal sequencing. Currently, purified Iss is being used to prepare hybridomas for production of monoclonal antibodies with the goal of evaluating anti-Iss as a reagent for the detection of virulent avian E. coli.