Blood in the semen due to a infection , irritation, trauma and tumor in any part of the reproductive tract starting from testicle and ending at the tip of the penis Most commonly due to infection and inflammation of the prostate.
For mor information please click the links:
http://www.askmen.com/sports/health/10_mens_health.html
http://www.nlm.nih.gov/medlineplus/ency/article/003163.htm
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