Deletions of the short arm of chromosome I I have been identified by both cytogenetic and molecular criteria in bladder and other types of solid tumor, indicating the presence of one or more suppressor loci in this region. To localize the I I p deletion target(s) more precisely and t o screen for loss of heterozygosity (LOH) on the long arm of the chromosome, I00 bladder tumors were analyzed for LOH on chromosome I I using restriction fragment length polymorphism (RFLPs) and microsatellite markers mapped to both I I p and I I q. Thirty-four tumors were found t o have LOH at I or more loci. Of these, I 7 had LOH restricted t o I I p, I 3 had LOH of both I I p and I I q, and 4 had LOH of I I q only. Eight tumors showed LOH at all informative loci indicating probable loss of an entire copy o f chromosome I I. A common region of deletion was defined on I I p between DllS922(1lp15.5)andDlIS569(1 lp15.1-15.2).Thisregiondoesnot includetheHRASor WI loci(at Ilp15.5and Ilp13, respectively). Seventeen tumors had LOH on I I q, 4 of which had LOH on I I q only. The common region of deletion on I I q was between FGF3 and DI IS490 (I Iq I3-q23.2). Two tumors showed LOH on both I I p and I I q with a clear region of retention of heterozygosity between, indicatinn the existence of two deletion targets on chromosome I I. Genes Chrornosorn