The immune response of precipitating antibodies and non-precipitating antibodies of high affinity (co-precipitating) of the IgG class was analyzed in rabbits repeatedly injected with egg albumin (as a soluble antigen) B. abortus-egg albumin and polymerized egg albumin (as particulate antigens). The results showed that the levels of anti-egg albumin non-precipitating antibodies induced by the soluble antigen were never higher than 10-15% of total antibodies throughout the experimental time. When particulate antigens were injected, the levels of non-precipitating antibodies increased up to 30-70% of the total antibody levels. This phenomenon is related to the way in which the antigen is available to the immune system (particle or aggregated), and is independent of the response induced by the particulate carrier. Components from the cell wall or bacterial membrane that could act as coadjuvants do not participate in this phenomenon. The results obtained seem to indicate that possibly there was a suppression of the synthesis of precipitating antibodies, and this would produce a relative increase in the non-precipitating antibodies.