Genetic alterations in 28 non-small cell lung carcinoma patients were detected on chromosomes 13q and 14q with microsatellite markers by polymerase chain reaction techniques. Loss of heterozygosity of up to 50% was detected with chromosome 13 markers and of up to 37% for chromosome 14. Microsatellite instability was as high as 30% on chromosome 13 and up to 19% on chromosome 14. Accumulated mutation frequencies of up to 94 and 93% were observed for chromosomes 13 and 14, respectively. Of eight tumors displaying high mutation frequencies, 1 also carried a K-ras mutation and 4 had p53 mutations. A significant association was observed between p53 mutations and genetic instability.