Patients 18 years of age or older with prostate cancer may be eligible for this study. Candidates will be screened with a medical history and physical examination, blood tests, bone scan if a recent one is not available, and possibly computed tomography (CT) and magnetic resonance imaging (MRI) scans of the pelvis. They will also have a liquid retention test, in which they are given an enema of 4 tablespoons of salt water that they must retain for 20 minutes.