An evaluation of longitudinal changes in PSA in men with and without prostate disease revealed that with age, the development of prostate disease is the most important factor influencing changes in PSA. Furthermore, the PSA changes with age are significantly different in men with and without prostate disease. The PSA velocity is greater in men with prostate cancer than in men with BPH and greater in men with prostate cancer and BPH than in men without any prostate disease. Thus, evaluation of PSA changes may help distinguish between men with prostate cancer and those without the disease. This idea will need to be confirmed prospectively. Finally, estimation of PSA doubling time from changes in PSA suggests that changes reflect prostatic growth. Therefore, PSA velocity could be of benefit in identifying men with prostate cancer that is destined to progress.