Antitumor activities have been reported for the aromatics Tonalide (6-acetyl-1,1,2,4,4,7-hexamethyl-tetrahydronaphthalene, AHTN) and Pearlide (1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta-γ-2-benzopyran, HHCB), which are contained in detergents. In this study, their carcinostatic activities in Ehrlich ascites tumor (EAT) cells were evaluated by mitochondrial dehydroganase-based WST-1 assay and dye-exclusion assay. The viability of EAT cells treated at 37 or 42°C for 30 min and sequentially cultured at 37°C was assayed at graded times. Immediately after treatment at 37°C, neither Tonalide nor Pearlide had an effect on EAT cells, even at a concentration as high as 200 µM. However, cell viability was reduced to 40% versus the control after 20 h of culture with Tonalide at 50 µM, and to below 20% at 25 µM after 72 h. In contrast, Pearlide was nearly inactive, even at a dose of 100 µM after 20 h of culture, and only reduced cell viability to 41.2% after 72 h. After treatment at 42°C without culture, neither of the aromatics was effective, even at a dose of 200 µM. The viability of cells cultured with Tonalide for 20 h after treatment at 42°C was reduced to nearly half of that at 37°C, and to 10% of the control after culture for 72 h. These values for the reduction of cell viability were also acheived by the Trypan blue dye-exclusion assay. The lifespan-prolonging effects of Tonalide on mice implanted with EAT cells were also examined. The lifespan of mice administrated 1.8 mg/day of Tonalide was prolonged by up to 28 days, while mice that did not receive Tonalide died within a mean of 15 days. Thus, Tonalide exhibited marked carcinostatic effects in vitro and in vivo and may prove to be a potent multipurpose antitumor agent in combination with hyperthermia.