The technical term for blood found in the semen is hematospermia. It can be caused by several different conditions that affect the tubes in the testicles which expel the semen from the scrotum. In addition to having blood present in the semen, other symptoms may include painful ejaculation, tenderness in the genital area, swelling of the testicles and/or groin and fever.
The most common of all conditions that cause blood to be present in the semen is inflamed prostate glands or inflamed seminal vesicles. However, it can also be a temporary situation due to a prostate injury (ex. prostate biopsy), sexual intercourse that is vigorous, delicate blood vessels or trauma to the testicles.
The type of treatment needed, if any, depends on the underlying cause. The majority of men who experience blood in their semen find that it is only temporary and clears up on its own. However, it is always a sound idea to get checked by a medical professional when something like this presents itself. This is especially true if the man is over forty years old, have burning with urination, find urinating difficult, are running a fever or have a history of cancer in the family.