The GFR-Vivo™ 680 imaging agent allows researchers to measure glomerular filtration rate noninvasively, in vivo in animals. GFR-Vivo 680, in combination with fluorescence molecular tomography imaging, can provide a noninvasive approach to generate consistent GFR measurements in animal models of kidney disease, dysfunction, and drug toxicity. This agent allows researchers to read out of GFR in vivo without the need for blood or urine sampling or labor intensive microplate assays. This fluorescent imaging agent is suited for researchers studying in vivo toxicology or drug safety assessment.