In an effort to identify genetic changes that may be the early hallmarks of epithelial cell overproliferation, we searched for p53 and nm23-H1 allelic deletions in oral benign epithelial lesions. In the study group were 25 benign epithelial lesions (lichen planus--17; leukoplakia--8; recurrent aphthous ulcers--2; one specimen diagnosed as benign migratory glossitis). Among 21 samples analysed for exon 4 (p53 gene) LOH, only 6 were informative, with no loss of either allele. OF 23 samples tested for LOH at intron 6 of p53 gene, 8 were informative, again with no presence of LOH. For nm23-H1 gene, the analysis was performed on a total of 24 cases. Of them, 16 were informative, however, none exhibited LOH at this locus. In conclusion, whereas the presence of gross gene alterations (LOH) would have been definitive evidence for the involvement of p53 and/or nm23 in the hyperproliferation process, the absence of LOH does not exclude the presence of either smaller mutations, altered regulation of normal gene, or dysfunction at the level of wild type protein. Alternatively, p53 and nm23-H1 may have no relation to oral lesion formation, and cannot presently be considered as an early step in benign, tissue transformation.