Blood in semen: Blood in semen (ejaculate) is also called hematospermia. Blood in semen can be caused by many conditions affecting the tubes that distribute semen from the testicles (seminal vesicles) or the prostate gland. The most common cause of blood in semen is inflammation of the seminal vesicles or prostate gland. Blood in the semen can temporarily be caused by injury to the prostate gland, such as from prostate biopsy.