A recombinant replication-deficient adenovirus has been generated that expresses a mutant of the Aquorea victoria green fluorescent protein (GFP) under the control of the strong CMV promoter by insertion into the E1 region (AdV-GFP). High expression of GFP was found in different cell types after infection with the recombinant virus that could be easily detected by fluorescence microscopy. In human umbilical vein endothelial cells (HUVEC), expression levels had already reached a maximum after 2 days and were stable for at least 7 days, as determined by Western blotting. As demonstrated by FACS analysis, up to 98% of HUVEC and approximately 70% of human smooth muscle cells could be transduced to express GFP. Since GFP can be detected in cells without the need for prior fixing and staining, the virus should be useful for optimizing in living cells the transduction efficiency of different cell types, of cells from different experimental animals, as well as studying the kinetics and persistence of adenovirus-mediated gene transfer in diverse experimental settings.