Beta-microseminoprotein (MSP) is one of the major proteins secreted by the prostate, and its biological role in tumorigenesis of the prostate has been postulated. We assigned the human MSP gene (MSMB) to 10q11.2 with fluorescence in situ hybridization using a phage clone that has an MSP gene insert. Our mapping data shows that the gene is outside the previously identified LOH-regions (10p and 10q24→qter) in prostate cancer cells and indicates that MSMB can be ruled out as a candidate for a tumor suppressor gene localized to those region