Although prostate cancer is the most common cancer diagnosed in men in this country, we do not know why some men develop this disease and others do not. In particular, we do not understand why, in some families, a high proportion of men are affected with prostate cancer. In such families, the determination of whether or not a male family member will develop prostate cancer is thought to result from what that person inherits from his parents. In other words, the factor that causes prostate cancer is most likely present in the genetic material (as an abnormal gene in the chromosomal DNA) in the sperm and/or the egg from which the individual develops. One can study prostate cancer in families to identify where in the DNA such genes are located using a technique called linkage analysis. Once the location is known, the gene itself can be identified and characterized to see how it causes the disease. This approach has been successfully used to locate and identify genes that cause cancers of the breast, colon, and kidney, but the genes that cause prostate cancer have not been identified, although the locations of several of these genes have been found. It is the goal of the proposed research to study prostate cancer families to find and characterize genes that determine genetic susceptibility for prostate cancer. The identification of prostate cancer genes will allow for the development of genetic tests to determine who is at high risk of developing prostate cancer and may eventually lead to better preventive, diagnostic, and therapeutic strategies to combat this common disease.