Willey Glover Denis (February 26, 1879 - January 9, 1929) was an American biochemist and physiologist. She was noted for her collaborations with Otto Folin studies of the protein metabolism. She was also a pioneer in the field of clinical chemistry and the measurement of protein in biological fluids (blood, urine and cerebrospinal fluid. She developed the first reliable method of assaying lead in urine, feces and tissue. She became the first woman to be elected a member of the Massachusetts General Hospital staff and her appointment as assistant professor at Tulane University may have made her the first woman to be appointed as a faculty member of a major medical institution in the United States. She died in 1929, at the age of 49, from complications from metastatic breast cancer.