The study of gene regulation has been greatly enhanced by the use of reporter gene systems such as beta galactosidase (P-gal), neomycin phosphotransferase (APH[3]11), chloramphenicol acetyl transferase (CAT), beta glucuronidase (GUS), and dihydrofolate reductase (DHFR). In the past several years, development of marker gene systems based on bioluminescence have extended the power of marker gene technology from enzymatic or color based in vitro assays to more sensitive single photon counting methods m vitro and in vivo A variety of proteins that catalyze bioluminescent reactions have been isolated and characterized. For several of these proteins, the genes are available and are currently being used as reporters for gene expression studies. Concomttant advances m single photon detection technology have recently made tt possible to measure gene expression nonmvasively m real time. We describe here the apphcatton of bacterial luciferase from Vibrio hawey i and eukaryotic luctferase from Renillu renifomzi s as markers for transformation and reporters of gene expression m transgemc plants. The major advantages of the luciferase gene expression system are its simplicity, sensitivity, safety for the investtgator and available nondestructive assay conditions, which permit real-time measurements of gene expression continuously throughout development of transgenic plants.