In this study we have adapted a well tried and sensitive fluorometric assay for DNA that uses m-diamino benzoic acid (DABA) for its reaction with deoxyribose which is cleaved by perchloric acid from DNA. We have confirmed that this is easily measured in human semen. The method has been used on 200 samples of semen from patients attending the Infertility Clinic and men attending before and after vasectomy to give a wide range of sperm density. The objective DNA estimation has been compared with sperm density measurement made by an experienced laboratory observer using the Makler chamber and making his observations in ignorance of the DNA estimations. There was good correlation between DNA concentration and sperm density. The experimental accuracy of the two methods was found to be comparable. The advantage of the method is its objectivity. However, its disadvantages are its cost in terms of time and material and it cannot be used to confirm post-vasectomy azoospermia because the method also measures DNA in leucocytes.