Mice were irradiated by the ETC (emission from a toroidal coil system) wave field proposed in our previous report, and the difference in physical stamina between irradiated and control (unirradiated) groups was examined. The mice were ETC-irradiated for 10 minutes a day. The mouse were fed 2g of feed per day, corresponding to about 1/2 of the sufficient quantity. The ETC irradiation continued for 6 days. A forced swimming test was begun on the eighth day and continued for 4 days. The feed quantity was reduced to Ig a day during the first 2 days of the forced swimming test, and increased to 2 g a day during the last 2 days. On the second day of the forced swimming test, both the irradiated and unirradiated groups showed a significantly lower rectal temperature than on the previous day. On the third day, the unirradiated group mice showed an increase in immobile time in the forced swimming test, and their mean value for the time was significantly greater than that of the irradiated group mice. This significant difference disappeared, however, after the feed quantity was increased to 2g. These findings implied that ETC irradiation improved the physical stamina of the extremely diet-controlled mice.