The finding that in many human tumors there is allelic loss and/or mutations in p53, in combination with recognition that these events may play a role in multi-stage carcinogenesis, has focused considerable interest on this gene. To help keep abreast of this rapidly expanding field, recent experiments on the role and potential regulation of p53 are described: these include discussions of p53 as an anti-proliferative agent, the p53 mutations found in human tumors and tumor cell lines, the conformational states of p53, phosphorylation of p53 by p34cdc2, and signals for the nuclear localization of p53. p53 may act as a transcriptional activator and the specific DNA sequences to which p53 protein binds are also discussed as is the importance of abrogation of p53 function in overcoming cellular senescence.