IFN-gamma is considered as a key factor in protection against heartwater of ruminants, caused by the obligate intracellular bacterium Ehrlichia ruminantium. In this study, a better definition of the molecular masses of IFN-gamma inducing proteins of the Gardel strain of E. ruminantium was obtained by the use of continuous flow electrophoresis (CFE) and sensitized polyclonal lymphocytes. Out of 15 E. ruminantium CFE fractions tested within the 14-39 kDa region, eight were commonly reacted to by all goats. Interestingly, half of these fractions fall within the 23-29 kDa region, shown previously to contain polymorphic B-cell epitopes. Thus, the results suggest that this region also contains T-cell epitopes potentially involved in protection. Also, several proteins were found to be more immunogenic than the serologically immunodominant MAP1 protein. Finally, high activity within the 15-19 kDa region was observed, which confirms previous work done with CD4+ T-cell lines obtained from cattle immunized with a South African strain of E. ruminantium. The proteins falling within the molecular weight ranges defined in this study may have potential as vaccine antigens.