Numerical changes of peripheral leucocytes after a hot-air room treatment was observed in guinea pigs during the 22 days' successive treatment. The results were as follows. 1. Number of various leucocytes was generally decreased after the hot-air room treatment, followed by recovery to the value before treatments during 22 days' observations. 2. Numbers of total leucocytes, lymphocytes and eosinophils, which were decreased after the treatment, gradually recovered to the value before treatments during the daily hot-air room treatment. On the other hand, the recovery of neutrophils or monocytes to the count before treatment was more rapidly. The value in numerical changes of neutrophils became smaller as the hot-air room treatments were performed for many days. 3. Numerical changes of basophils and Kurloff cells did not show any definite tendency after the hot-air room treatment. 4. Numbers of total leucocytes, neutrophils, lymphocytes and eosinophils were increased and monocyte count was slightly decreased after the 22days hot-air room treatment. No
change was observed in the counts of basophils and Kurloff cells.