E. coli Protein (ECP) is defined as a group of proteins that originate in the E. coli host cell used during fermentation for Retavase™ manufacture. ECP is cleared by a series of downstream purification steps during the Retavase manufacturing process. This poster summarizes the sampling plan, analytical method, and results that demonstrate clearance of the ECP host cell protein in the Retavase purification process. A total of 202 samples from each downstream purification step were taken over 7 consecutive Retavase batches. Samples from 3 of the 7 batches were analyzed for ECP content by Enzyme-Linked Immunosorbent Assay (ELISA). ECP trending data was generated for the major purification steps including affinity chromatography (ETI), cation exchange chromatography (TSK), anion exchange chromatography (Q), and concentration (UF/DF) steps. The data shows that the ETI and TSK chromatography steps contribute the highest levels of ECP clearance. The majority of ECP in product eluted at these steps is found in the earlier parts of the elution peaks. The Q chromatography and UF/DF steps contribute minimal ECP clearance.