Loss of the chromosomal region 10q23-25 is a frequent event in the progression of prostate adenocarcinoma. A candidate tumor suppressor gene from this region, Mxi1 at 10q25, has recently been shown to be mutated in a small number of prostate tumors. To more strictly define those regions of 10q loss that are likely to be involved in tumor advancement, we have constructed a detailed deletion map spanning 10q23-25 that incorporates Mxi1. Sixty-two % (23 of 37) of tumors analyzed exhibited some degree of 10q23-25 loss. Our data suggest the presence of a prostate tumor suppressor gene(s) near the 10q23-24 boundary, which was deleted in the overwhelming majority (22 of 23) of tumors showing loss. In contrast, specific loss of Mxi1, as opposed to loss of other 10q23-25 regions or of the entire region, was observed in only 1 of 23 tumors and was accompanied by loss of markers at the 10q23-24 boundary. Furthermore, we failed to detect any mutations in Mxi1 in those tumors showing Mxi1-associated marker loss by either single-strand conformation polymorphism analysis or direct DNA sequencing.