The pathogenicity and immunogenicity of Eimeria intestinalis was evaluated in SPF rabbits. The animals were given immunizing doses of 6, 6 x 10(2), 6 x 10(3), and 6 x 10(4) sporulated oocysts and were challenged with 3 x 10(3) oocysts. The criteria analysed were the daily weight gain and the oocyst output. This study showed that E. intestinalis had strong immunogenicity, as the inoculation of 6 oocysts was sufficient to minimize the clinical expression of the disease following the challenge and to reduce the oocyst output by about 60%. The immunity towards the excretion of oocysts and the illness was absolute in animals inoculated with 600 or more oocysts. Moreover, this protection seemed to be efficient at least 8 weeks after the challenge. The present results also confirm the pathogenicity of E. intestinalis, although the occurrence of diarrhoea may be irregular, and emphasize the fact that the capacity of this Eimeria for multiplication is not a criterion for clinical diagnosis of the disease.