A preliminary quantitative study on the population growth rate of Theileria parva in the bovine host failed to confirm the constant growth rate independent of size of infective dose reported by earlier workers. Experiments in methodology were performed therefore to standardize the techniques for obtaining (a) accurate estimates of infection rates from biopsy smears, (b) representative samples from a superficial lymph node source. A further experiment was carried out to establish that such samples were representative of the total parasitic biomass. These techniques were applied in a wider ranging quantitative study using four infective doses at ten fold intervals for infecting animals. The resultant growth rates were again dependent on the size of the infective dose. A definitive experiment, using five infective doses at ten fold intervals confirmed the divergence of growth rates. It was also shown that the severity of the clinical reaction, and the survival time was dependent on the size of the infective dose. The implications of these results in relation to immunization of cattle against T. parva are discussed. The standardized methods were applied also in a chemoprophylactic study to observe the growth rates of T. parva as affected by different regimens of tetracycline. Other possible applications of these standardized methods are discussed.