Setting up breeding programs for transgenic mouse strains require to distinguish homozygous from the heterozygous transgenic animals.The combinational use of the fluorescence reporter transgene and small animal in-vivo imaging system might allow us to rapidly and visually determine the transgenic mice homozygous for transgene(s) by the in vivo fluorescence imaging.RLG,RCLG or Rm17LG transgenic mice ubiquitously express red fluorescent protein (RFP).To identify homozygous RLG transgenic mice,whole-body fluorescence imaging for all of newborn F2-generation littermates produced by mating of RFP-positive heterozygous transgenic mice (F1-generation) derived from the same transgenic founder was performed.