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There has been an increasing interest in manure anaerobic digestion; however, economic constraints are still one of the limits to widespread use of the technology in the United States. Co-digestion of manure with other feedstocks has been noted as a way to increase the economic feasibility of animal feeding operation anaerobic digesters via increased energy production potential. A wide variety of materials have been proposed as co-digestion materials, and additional substrates will continue to receive consideration. Biochemical methane potential assays (BMPs) have been reported to provide a "first-cut" evaluation of potential substrates. This article provides specific details about the BMP assay process used by the Agricultural Waste Management Laboratory (AWML) at Iowa State University (ISU) on agricultural materials and by-products, including the assay method and utilization of the results. Additionally, BMP results from 31 samples assayed in the ISU AWML as broader anaerobic digestion research or as service to the industry have been included. Results showed that the high solid content and non-homogeneity of agricultural materials and by-products can increase variability in assay results. The method utilized here helped limit the effects by utilizing volatile solids concentrations instead of chemical oxygen demand to initiate the BMP assays and to normalize the results. The coefficient of variation for the assays performed in triplicate ranged from1.6% to 33% in which the majority was less than 15%. For five of the substrate types analyzed (beef manure, dairy manure, cheese when lactate permeate, food processing marinate, and enzyme process by-product), multiple samples were assayed from different sources. The sample standard deviations indicated that methane production potential could be affected by material source and that BMP assays reported here should only be used as an estimate when considering which types of materials to assay.