Studies upon the seminal fructose, as the chief subject, have been carried out in male infertility with their clinical signs and the experiments on man and rats have also been carried out to pursue the effects upon the vasectomy. 1. Of 153 male infertility, 50.3% was azoospermia, 12.4% was oligozoospermia and 3.9% was necrozoospermia. The abnormal objective signs were observed in testis. epididymis, prostate and seminal vesicles. 64.9% were observed in azoospermia, 26.3% in oligozoospermia and 50.0% in necrozoospermia. 2. Epididymitis tuberculosa (3.9%) and epididymitis gonorrhea (30.5%) were observed in past history and inflammation of epididymis seems to have an important effect upon the secretory function of male accessory organs. 3. More detailed examinations have been carried out in 16 patients on oligozoospermia and azoospermia. The Volme of semen, seminal fructose, testicular biopsy and vesiculograms were examined and found no relation between the values of seminal fructose and the atrophy of seminiferous tubulus, whereas the most intimate connections were observed upon the development of the seminal vesicles. 4. Various values of the examinations on the volume of semen and the concentration of seminal fructose were observed in patients with urogenital diseases. Upon the tuberculoses of seminal vesicles, the values were found in high and on the cysts of seminal vesicles were found in low. 5. Upon the effects of vasectomy on normal man, the values of seminal fructose were decrease after a week period of operation and radually return to normal, whereas in rats and rabbits, the values were found unstable after the operation, but, in general, these were disposed to decrease. 6. From these above point of views, the seminal fructose on male infertility and urogenital disease seems to be controlled by the state of the seminal vesicles, and the male sexual hormones seem to have the close relation upon the secretory function.