Fluorescence lifetime imaging (FLIM) has been reported for a single halobacterium loaded with 2',7'-bis-(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). FLIM of halobacteria exhibits two distinct fluorescence lifetimes, representing different environments from each other in different halobacteria. The observed difference in the fluorescence lifetime appears to be due to the difference in electric field inside a cell. Fluorescence intensity of BCECF in polyvinyl alcohol film is quenched by an external electric field, indicating that the fluorescence lifetime of BCECF is affected by an electric field. (c) 2007 Published by Elsevier B.V.