The objectives of this slide presentation in relation to interlaboratory validation of USEPA Method 1600 (mEI) for enterococci in wastewater effluent were to: assess method performance in the matrix of interest; develop quantitative quality control (QC) acceptance criteria in a reference matrix to support future assessments of laboratory performance; and, develop quantitative QC acceptance criteria in the matrix of interest to support future assessments of method performance. Matrices evaluated included: reference matrix, phosphate buffered saline (PBS); and, wastewater matrices (disinfected effluent and secondary effluent). Topics covered include: study design consisting of study schedule, sample analyses, participant laboratory quality control analyses; data reporting and validation consisting of standardized data checklist; method performance consisting of unspiked sample results (n=44), overall false positive and false negative confirmation rates, weighted false positive and false negative rates, spiked PBS results, spiked wastewater results, follow-on verification study results; quantitative QC acceptance criteria consisting of IPR and OPR, MS and MSD.