Allelic mutation on chromosome 19 has previously been reported as a frequent genetic event in human glial tumors. In an effort to localize specific regions of importance on this chromosome better, 13 highly polymorphic genetic markers distributed along the length of chromosome 19 were used for evaluation of loss of heterozygosity (LOH) and microsatellite instability in a total of 100 brain tumors, including 75 astrocytomas (55 grade 4; 7 grade 3; 5 grade 2; 6 grade 1; and 2 other), 17 oligodendrogliomas (1 grade 4; 5 grade 3; 10 grade 2; and 1 grade 1), and 8 mixed oligoastrocytomas (MOA) (3 grade 4; 2 grade 3; and 3 grade 2). No microsatellite expansion was observed in these glial tumors for any of the chromosome 19 loci examined. LOH for loci on chromosome 19 was detected in 23/74 informative astrocytomas (31%), 11/17 oligodendrogliomas (65%), and 3/8 MOA (38%). Partial deletion of chromosome 19 occurred more frequently (31/37 cases) than did loss of one whole copy of the chromosome, and a morphology-specific pattern of LOH was observed. In 12/14 (86%) instances of chromosome 19 deletion in oligodendrogliomas and MOA, the 19q arm showed LOH, whereas the 19p arm showed no loss for all informative loci. Conversely, in 17/23 (74%) instances of chromosome 19 deletion in astrocytomas, the 19p arm showed LOH, whereas the 19q arm showed no loss for one or more loci. Thus, loss of 19q and retention of 19p are strongly associated with oligodendroglioma and MOA, whereas loss of 19p and retention of distal 19q is associated with astrocytoma.(ABSTRACT TRUNCATED AT 250 WORDS)