The effect of retinoid-induced suppression of in vitro invasive ability of A549 human lung carcinoma cells on p53 gene expression and cytokeratin (CK) 18 level was investigated. Induction of suppression of cell invasion was accompanied by an increase in amounts of p53 mRNA and protein and a decrease in CK18. Moreover, the p53 mRNA and protein levels increased coordinately with time in relationship to the degree of invasion-suppression. The results indicate that p53 expression is involved in alteration of the lung cell metastatic phenotype, and that p53 is an important marker for this process.