The reaction of the tissues to an infection with Cysticercus bovis was studied on material from cattle with a spontaneous and an experimental infection. The authors examined a total of 232 cysts from the skeletal muscles. A tissue reaction to C. bovis was inflammatory in nature and originated always at the site at which the invaginated scolex opened into the surface. Typical of these changes were the origin of a pseudoepithelial rim and a zone of granulation tissue maturing on the periphery. At a later phase marking the start of necrotic changes in the cysticercus, the inflammation accompanied by exudation started to develop anew. Calcified structures stirred up a giant cell, cleaning up reaction, and cicatrization followed the resorption of the parasite and the exudate. We identified two types of necroses in a tissue reaction to C. bovis: a focal necrosis of the exudate and the inflammatory rim with a subsequent dystrophic calcification, and a focal necrosis and calcification of collagenous fibres and their groups. Necrotic-like foci typical of a reaction to C. bovis were seen in the inflammatory rim. Using specific staining procedures, we succeeded in distinguishing these foci which did not succumb completely to a dystrophic calcification, from concomitantly present necrotic foci.