The 1925 serum run to Nome, also known as the Great Race of Mercy and The Serum Run, was a transport of diphtheria antitoxin by dog sled relay across the U.S. territory of Alaska by 20 mushers and about 150 sled dogs across 674 miles in 5+1⁄2 days, saving the small town of Nome and the surrounding communities from a developing epidemic of diphtheria. Wikipedia