In a paper recently published we described a fibro-adenoma of the breast which, when assayed, yielded a relatively great amount of estrogenic principle. Because of this finding we were prompted to assay a uterine fibroid to determine whether the estrogenic principle, the follicle-stimulating factor and the luteinizing principle might be found in this type of tumor. A hysteromyomectomy was performed on a patient whose history will be given later. The fibroids were removed, care being exercised that no mucous membrane was included in the tumor. The material was forwarded to Dr. J. H. Morrell of the E. R. Squibb and Sons Laboratory for a bio-assay. Dr. Morrell reported that the tissue contained 4½ rat units of the follicle-stimulating and luteinizing factors per gram of desiccated tissue. The extract of the tissue gave both effects. This material was tested by the same technicians who are standardizing the preparation of the