p16MTS1/INK4A negatively regulates cell cycle progression by inhibiting the cyclin D/CDK4 complex that phosphorylates pRb. Frequent homozygous deletions of the p16 gene were recently found in various tumor cell lines. We examined the relationship between the genetic status of p16 and the expression of the cell cycle regulating molecules in human esophageal carcinoma cell lines. Out of eight human esophageal carcinoma cell lines, seven (67.5%) and six (75%) cell lines showed homozygous deletions of the p16 and p15 genes, respectively. All the p16-negative cell lines expressed high levels of cyclin D1, CDK4 and p27KIP1 proteins. Interestingly, the expression level of cyclin D1 was closely correlated to the levels of not only CDK4 but also p27KIP1 protein in p16-negative cell lines. Furthermore, all the p16-negative cell lines expressed Rb protein of approx 110 kDa which corresponds to the phosphorylated form, whereas the cell line with intact p15 and p16 genes did not express pRb. These results suggest that the expression of cyclin D1, CDK4, Rb and p27 is associated with the p16 gene status in esophageal carcinoma cell lines. Alternatively, loss of the p16 gene and subsequent over-expression of cyclin D1 and CDK4 might be involved in autonomous growth of esophageal carcinoma cells.