Fatal accidents during butane abuse frequently occur in Japan and in many countries around the world. Although analytical data about butane concentration in postmortem samples is being accumulated, when using the data to determine the cause of death, careful interpretation is required because the gas is easily diffused. Two fatal butane poisoning cases were encountered, and butane quantification of autopsy samples obtained from left and right heart blood, femoral blood, kidney, liver, lung, brain and fatty tissues was performed. In both cases, butane concentration in the left heart blood was lower than in the right heart blood or the femoral blood, despite gas inhalation. These findings may indicate that the deceased individuals interrupted gas inhalation and inhaled room air immediately before their death, therefore ruling out asphyxia due to anoxia as the mechanism of death. Case 1, which was suspected to be a not acute death, showed a very high butane concentration ratio of fatty tissues to femoral blood of over 70. Case 2 was considered an acute death, and the butane concentration ratio of fatty tissues to femoral blood was 8.2. These results are consistent with previously reported findings showing that much higher ratios of fatty tissues to blood are compatible with long survival time. In conclusion, the comparison of butane concentration among different samples, including left heart blood versus right heart blood and fatty tissues versus blood, is useful when interpreting the result of postmortem butane analysis to examine the mechanism of death and survival time.