What is the normal level of PSA (prostate specific antigen) in males?

Normal PSA level is less than 4 ng/ml. Prostate-specific antigen (PSA) is an androgen regulated serine protease produced by the prostate epithelium. It is normally present in low concentrations in the blood of all adult males. PSA levels may be elevated in the blood of men with benign prostate conditions such as prostatitis and benign prostatic hyperplasia, as well as in men with prostate cancer. It is useful in evaluating the effectiveness of prostate cancer treatment and monitoring for recurrence after therapy.