NMR spectroscopy can be used to identify and determine various molecular species in organs and tissues, and can provide information on the condition of their presence. We used NMR spectroscopy to examine postmortem changes in rabbits. ATP levels could be determined with ATP beta-position phosphorus atom signals in 31P-NMR spectra of tissue samples used as parameters. Changes over time in myocardial and limb muscular ATP levels were examined from just after death due to various causes to 7 hours after death, and the following results were obtained: 1. Myocardial ATP levels were low in groups with pronounced anoxia just before death. 2. Among groups with identical causes of death, decreases in myocardial ATP levels were larger the more pronounced was anoxia. Findings 1 and 2 are applicable to determination of acute cause of death considered otherwise difficult to detect in legal medical practice. 3. The decrease in ATP level just after death was smaller in limb muscles than in myocardium, and changes over time in the decrease in ATP after death could be observed. This finding may be applicable to the estimation of passage of time after death, a problem of great import in legal medicine.