Resveratrol (trans-3,4′,5-trihydroxystilbene) is a naturally occurring polyphenolic phytoalexin found in grapes, and has been shown to inhibit the growth of various types of cancer cells. We investigated the mechanism of the antiproliferative effect of resveratrol in A431-transformed keratinocytes harbouring mutant p53, and show that it is ccompanied by G1 cell cycle arrest, which coincides with a marked inhibition of G1 cell cycle regulatory proteins, including cyclins A and D1 and cyclin-dependent kinase (CDK)6 and p53-independent induction of p21WAF1. Cell cycle arrest was also associated with the accumulation of hypophosphorylated Rb and p27KIP1. Resveratrol inhibited mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK)1 > extracellular signal-regulated protein kinase (ERK)1/ 2 signalling, downregulated c-Jun, and suppressed activating protein (AP)-1 DNA-binding and promoter activity. In addition, the inhibition of MEK1 > ERK1/2 signalling appears to be independent of retinoblastoma protein (pRb) hypophosphorylation in A431 cells, as PD098059 did not suppress pRb phosphorylation. Our results demonstrate that resveratrol affects multiple cellular targets in A431 cells, and that the downregulation of both AP-1 and pRb contributes to its antiproliferative activity in these cells. © The Authors 2006. Journal compilation © 2006 Blackwell Munksgaard.