Cytogenetic and molecular analyses of primitive neuroectodermal tumors (PNETs) of the central nervous system (CNS) have demonstrated material losses of 17p, the region that contains the TP53 gene, as the most frequent abnormality. Mutations in the TP53 gene are, however, very rare in these tumors. These findings strongly suggest that another, as yet unidentified, gene on 17p may be involved. We performed a search for loss of heterozygosity (LOH) on 17p by microsatellite markers on 26 childhood CNS tumors as well as TP53 gene mutations (exons 5-8) by single-strand conformational polymorphism analysis on 41 pediatric brain tumor samples of distinct histologic types. LOH was detected in 10 cases: 7 PNET, 2 astrocytomas, and 1 glioblastoma multiforme. In 4 of the PNETs the losses were limited to more distal markers. On the other hand, TP53 mutations were detected in 6 of 41 samples studied. Our results not only confirm the low penetrance of the TP53 gene on pediatric CNS tumors, but also provide further evidence of a putative tumor suppressor gene distal to TP53, between markers (D17S938, D17S926) and 17pter, specifically taking part in the development of PNET.