The four distinguished German men of science to whom the following biographical notes relate: Robert Koch (1843–1910), Paul Ehrlich (1854–1915), Emil von Behring (1854–1917), and Friedrich Loeffler (1852–1915), form a group of singular interest because of the relations that existed between them and the various problems to the solution of which they devoted their remarkable talents and energies. Each of them has left an indelible mark upon the annals of research and discovery in relation to infective diseases of man and animals, their etiology, prevention and cure. If it were at all possible to reckon up the sum of human and animal lives that they have saved from premature extinction through their collective efforts, direct and indirect, the total would attain gigantic proportions. Mankind should ever keep these men in grateful memory.