p53 is among the most intensely studied human proteins because of its vital role as the prototype tumor suppressor. As a result, there are widespread applications for p53 functional analysis in biotechnology as it relates to cancer research. p53 is a potent sequence specific transcription factor, which induces the expression of a number of genes whose products mediate cell cycle arrest and apoptosis. Because the tumor suppressor activity of p53 is dependent on its transcription regulatory function, we have undertaken to develop a p53-responsive green fluorescent protein reporter strategy to enable the identification of live cells containing p53 transcriptional transactivation activity. We demonstrate within the use of GFP fluorescence to monitor both endogenous and plasmid derived p53 biochemical and biological activity. Identifying live cells with p53 activity through GFP fluorescence will have wide application for both in vitro and in vivo studies of the p53 tumor suppressor protein. (C) 2000 Elsevier Science B.V. All rights reserved.