The history of bovine anaplasmosis, or tick-born gallsickness, since the discovery of Anaplasma marginale by Sir Arnold Theiler is briefly reviewed. The development of the Anaplasma centrale vaccine by Theiler, up to the composition of the present vaccine issued by Onderstepoort in which the original isolate is still passaged, is discussed in detail. Recent transmission studies at Onderstepoort have shown that 5 tick species are capable of transmitting anaplasmosis intrastadially, and intrastadial transmission, especially by adult male ticks, it is believed, could play an important role in the epizootiology of bovine anaplasmosis in South Africa. Disease incidence and tick distribution are discussed in relation to enzootic and epizootic conditions. Investigations have proved that the Onderstepoort A. centrale vaccine is not as avirulent in adult cattle as it was previously thought to be. The results of a field trial undertaken to test the infectivity of the vaccine, are given.