Experiments are described to examine the pathogenesis of anaplasmosis in Bos indicus cattle with particular emphasis on nutrition, breed and age. The disease seemed to be less severe in animals under a poor plane of nutrition. Breed was shown to have little effect and there was an age resistance. Natural transmission in Bos indicus calves occurred with ease in endemic areas. This indicated that the introduction of Bos indicus cattle should not adversely affect enzootic stability.