Twenty-four Harderian glands from 16 transgenic mice carrying a v-Ha-ras gene under the control of the mouse mammary tumor virus promoter were examined histologically upon death of the animals. Eight glands were histologically normal and eleven were hyperplastic. Four additional glands showed predominantly hyperplasia, but also contained foci of dysplasia and in situ carcinoma. One gland contained an adenocarcinoma. The range of pathology observed in the Harderian glands of these transgenic mice was similar to that which arises spontaneously, although hyperplasia, and not adenoma, occurred in these mice as the benign tumor.