Biological changes induced by the noise have been studed by various investigators, but many subjects are still in question. The author observed the changes in blood of hamsters exposed to the noise for a long duration. Six hamsters were used as experimental animals, and were exposed to the band noise (average 2,000 Hz, 100-110 Phone) 6 hours a day for 4 weeks, and five hamsters were used as a control group. The results observed are as follows ; 1) RBC counts were increased, and WBC counts were decreased in the noise-exposed group. Neutrophils increased, lymphocytes and eosinophils decreased in the noise group. 2) Hemoglobin value was raised slightly in the noise-exposed group. 3) Cholesterol contents were slightly higher in the noise-exposed group than in the control group.