The study found that each of the compounds tested would be a suitable internal standard in the analysis of fire debris. The internal-standard candidates (ISCs) tested were toluene-d8 (perdeuterotoluene), tetrachloroethylene (perchloroethylene), chlorobenzene (phenyl chloride), styrene-d8 (perdeuterostyrene), naphthalene-d8 (perdeuteronaphthalene), diphenyl-d10 (1,1’-biphenyl-d10), n-octylbenzene (1-phenyl octane), and 3-phenyl toluene (3-methyl-1,1’-biphenyl). Ideally, an internal standard for fire debris analysis should be a compound that is not commonly found in pyrolysis, combustion, or distillation products normally present in fire debris or in an ignitable liquid; it should elute within the typical boiling range of the compounds normally present in fire debris and ignitable liquids; it should have a sufficiently unique mass spectrum so it can be extracted from a total ion chromatogram obtained from the analysis of fire debris; and it should be cost-effective. Based on the testing results, the authors recommend that the internal standard be delivered to the fire debris either in solution, with the internal standard diluted in the same solvent used to elute the charcoal strip, or by spotting the internal standard directly on a piece of filter paper that is then placed into the evidence container. The authors favor the use of two internal standards in combination, one with a low boiling point and one with a higher boiling point. Tetrachloroethylene is favored for the low boiling internal standard. For the higher boiling internal standard, the authors recommend naphthalene-d8. Descriptions of materials and methods address standards and reagents, gas chromatography-mass spectrometry conditions, extraction efficiency, evaluation of ISCs in the presence of different ignitable liquids, and evaluation of ISCs in the presence of fire debris. 6 tables, 4 figures, and 18 references