Kerner equation for motion in a non-Abelian gauge field

The equations of motion of an isospin-carrying particle in a Yang-Mills and gravitational field were first proposed in 1968 by Kerner, who considered geodesics in a Kaluza-Klein-type framework. Two years later the flat space Kerner equations were completed by considering also the motion of the isospin by Wong, who used a field-theoretical approach. Their groundbreaking work was then followed by a long series of rediscoveries whose history is reviewed. The concept of isospin charge and the physical meaning of its motion are discussed. Conserved quantities are studied for Wu-Yang monopoles and for diatomic molecules by using van Holten's algorithm.