160 mice of the BALB/C strain of both sexes, aged 3 months, were divided into four equal groups out of which two were regularly irritated by a combination of an optical signal and electrical stroke. After one month of irritation one nonirritated and one irritated group were whole body irradiated with a single dose of 6.65 Gy (1.83 Gy/min), the other two groups were sham irradiated. The mice lived until their spontaneous death or one year after irradiation, respectively, when the rest of the animals were sacrificed. The appearance of malignant tumors was noted. Irradiation shortened the survival time while the irritation had an appeasing, compensatory effect, more expressed in the males than in the females. After irradiation the number and assortment of the tumors increased and the latent period essentially shortened. In the irritated animals the number and assortment of the malignant tumors were reduced and a tendency for lengthening of the latent time period was seen; these differences, however, were not statistically significant. In spite of some differences the response in both sexes to irradiation and irritation or their combination was similar.