In this study, researchers reviewed data from 3,040 men (909 African American men and 2,131 whites). Every man had received both a prostate specific antigen test (PSA) and a digital rectal examination or a negative prostate biopsy. None had known prostate cancer. Up to the age of 40, there was no difference between African American and white males in serum PSA levels. Then mean PSA levels in African Americans started to rise. From 50 to 59, the African Americans' mean average was 2.4 ng/ml, as compared to 1.64 ng/ml in whites. From 60 to 69, African American men's mean was 5.8, compared to 3.21 for whites. Between 70 and 79, the African American men's mean hit 9.84, compared to 3.47 for whites. The investigators conclude that racial variation in PSA is detected in all decades above the age of 40.