THE occurrence and possible function of the neuraminic acids in mammalian tissues and fluids is a matter of great interest. Large amounts of N-acetylneuraminic acid have been demonstrated in the seminal fluid of man1,2, bull3 and boar4. Analysis of the secretions of the accessory genital organs of the boar showed that the mucin from the bulbourethral glands contained 4–4.5 per cent (fresh weight) of neuraminic acid. The concentration was less in the seminal vesicles and negligible in the other glandular secretions5. In man the average concentration of neuraminic acid was in the seminal vesicle fluids 231.9 mg/100 ml., in the prostatic secretions 60.6 mg/100 ml., and in the seminal fluid 124.2 mg/100 ml. From these data, Warren2 calculated that approximately two-thirds of the seminal fluid came from the prostate gland. It is, however, difficult to calculate the relative contribution of the various glandular systems to the ejaculate by using data obtained from extracts of autopsy material.