To identify chromosomal loci of tumor suppressor genes involved in the genesis and progression of non-small cell lung carcinoma (NSCLC), comparative allelotype analysis was performed in 23 stage I primary lung tumors and in 22 metastatic lung tumors t o the brain. In total, 84 loci on all 22 autosomal chromosomes were examined for loss of heterozygosity (LOH) by restriction fragment length polymorphism (RFLP) analysis with 40 polymorphic DNA probes and polymerase chain reaction (PCR)-LOH analysis of 44 polymorphic loci. LOH on chromosome arms 3p, I 3q, and I7p was detected frequently (>60%) in both stage I primary lung tumors and brain metastases, whereas the incidence of LOH on chromosome arms 2q, 5q, 9p, I2q, I8q, and 22q was more than 60% only in brain metastases. In particular, the incidence of LOH on chromosome arms 2q, 9p, I8q, and 22q in brain metastases was significantly higher than that in stage I primary lung tumors (P < 0.05). These results indicate that tumor suppressor genes on chromosome arms 3p, I3q, and I7p are involved in the genesis of NSCLC, whereas those on several chromosome arms, especially on 2q. 9p, 18q and 22q, play an important role in the progression of NSCLC. Genes Chromosom Cancer I7:7 1-77 ( I 996). 0 I996 Wiley-LiA, Inc.