Embalming is common, and yet it can create problems for the forensic scientist if a drug has been the cause of death and if this drug is also reactive toward the embalming fluid. Previous studies have focused on the amines such as nortriptyline, desipramine, and fenfluramine. In the presence of formalin, a typical component of embalming fluid, these compounds can be rapidly converted to their methylated derivatives amitriptyline, imipramine, and N-methyl-fenfluramine, respectively. We have begun a larger project designed to determine the reactivity and reactions of a wide range of drugs with formalin and have extended it to amphetamines. We report here our results from methamphetamine, which is converted into its N-methyl derivative in the presence of formalin. The rate of conversion is dependent upon pH and formalin concentration with the greatest conversion occurring under basic conditions and the highest formalin concentration. Up to 100% conversion in 24 h was observed under certain conditions. When studied in human tissue exposed to methamphetamine and treated with formalin, again, conversion to N-methyl-methamphetamine was readily apparent as early as 30 min after exposure to formalin. Finally, we note that the reactions of methamphetamine with formalin studied here are probably general and should be considered when performing postmortem/postembalming forensic analysis.