Chromosome 11p15 deletions occur frequently in several types of human cancer, both sporadic and familial, suggesting that a tumor suppressor gene is present within the deleted chromosome region. We carried out a restriction fragment length polymorphism analysis of chromosome 11p in two types of human brain tumors: malignant astrocytoma, the most common glial tumor in adults; and primitive neuroectodermal tumor (PNET), a malignant embryonic tumor that afflicts children. Loss of heterozygosity was found in 11/43 malignant astrocytomas (26%) and in 3/11 PNETs (27%). Deletion mapping revealed a region of loss on chromosome 11p (p15.4-pter) that was common to both tumor types. To determine whether the c-H-ras gene, located on chromosome 11p in the common region of deletion, was a candidate gene, we analyzed polymerase chain reaction products corresponding to all four c-H-ras coding exons for single-strand conformation polymorphisms. The absence of electrophoretic mobility shifts in tumor DNA compared to leukocyte DNA indicated that c-H-ras gene mutations were most likely not present. These results suggested that loss of a gene on chromosome 11p15 distinct from c-H-ras is an important step in tumorigenesis within the central nervous system in both children and adults.