A dramatic change occurs in the cellular microenvironment during cell stress, but it has been difficult to follow these changes in vivo. Here, fluorescence lifetime imaging (FLIM) microscopy has been used to examine stress-induced changes in the microenvironment in a single cell. It is observed that the fluorescence lifetime of HeLa cells expressing an enhanced green fluorescent protein (EGFP)-tudor fusion protein changes under stress. The change in the fluorescence lifetime appears to be due to an alteration in the local electric field in the protein matrix surrounding the chromophore of EGFP. In fact, the fluorescence lifetime of the GFP chromophore in a polyvinyl alcohol film is found to decrease in the presence of an electric field, based on the measurements of the field-induced change in the fluorescence decay profile. The results indicate that the rate of the non-radiative process of the chromophore of GFP is enhanced by an applied electric field. The FLIM method allows noninvasive determination of the status of the individual cells.