We successfully cultivated the rickettsia Cowdria ruminantium, in bovine endothelial cell lines (Bovine Umbilical Endothelial Cells/BUEC and Bovine microvasculature Cells/BMC) and also in primary endothelial cells of bovine origin (Bovine Aorta Endothelial cells/BAEC) and more surprisingly in cells of human origin--Human Umbilical Vein Endothelial Cells/HUVEC--and Human Endothelial Cells from the Microvasculature/HEMEC. This first evidence of the pathogenicity of this bovine rickettsia in the human cell system gene-rates new interest as regards its possible relevance for human health. It provides also further possibilities for the attenuation of Cowdria ruminantium isolates, and therefore brings new prospects for vaccine preparation. In vaccine production, mass cell culture is essential. Our results indicate that endothelial cells attach efficiently on collagen microspheres. As BAEC cells grow well on them in a batch mode, and if the process could be optimized for the different cell types (using appropriate adhesion and growth factors) our observations offer interesting prospects for the future development of a Cowdria ruminantium vaccine production in the fluidized-bed reactor VERAX System one, which provides easy control of growth conditions.