The fluorescent tracer agent 3,6-diamino-2,5-bis{N-[(1R)-1-carboxy-2-hydroxyethyl]carbamoyl}pyrazine, designated MB-102, has been developed with properties and attributes for use as a direct measure of glomerular filtration rate (GFR). In comparison to known standard exogenous GFR agents in animal models, MB-102 has demonstrated an excellent correlation. A battery of toxicity tests has been completed on this new fluorescent tracer agent, including single dose toxicity studies in rats and dogs to determine overall toxicity and toxicokinetics of the compound. Blood compatibility, mutation assay, chromosomal aberration assay, and several other assays were also completed. Toxicity assessments were based on mortality, clinical signs, body weight, food consumption and anatomical pathology. Doses of up to 200–300 times the estimated human dose were administered. No test-article related effects were noted on body weight, food consumption, ophthalmic observations and no abnormal pathology was seen in either macroscopic or microscopic evaluations of any organs or tissues. All animals survived to scheduled sacrifice. Transient discoloration of skin and urine was noted at the higher dose levels in both species as expected from a highly fluorescent compound and was not considered pathological. Thus initial toxicology studies of this new fluorescent tracer agent MB-102 have resulted in negligible demonstrable pathological test article concerns.