The high incidence of loss of chromosome 10 alleles in glioblastoma multiforme suggests the presence on this chromosome of a tumor suppressor gene that is important in glioma tumorigenesis and progression. Our initial deletion mapping studies using restriction fragment length polymorphism markers indicated a common deletion region in 10q24-qter. In an attempt to localize the deleted region further, we screened a panel of 117 gliomas for loss of heterozygosity for chromosome 10 loci using 10 microsatellite markers. Seventeen tumors showed partial loss of a copy of chromosome 10 and were further analysed using 28 additional microsatellite markers. Of these, 10 had terminal deletion in the q arm, three had deletions in both p and q arms, two contained interstitial deletion in 10q and two carried deletions in 10p. In the 15 tumors with deletions in 10q, the minimal overlapping deletion region was in distal 10q between markers D10S587 and D10S216. Loci D10S587 and D10S216 are approximately mapped to a 5 cM region in 10q25.1.