Lazzarini (3) was one of the first to make use of the methods of tissue culture in the study of the nature of cells of blood vessels. His pioneer work was continued and extended by Pollack and his group (5). Like any other new approach this also had been vigorously discussed until recently. At the present time a large amount of evidence has been made available from the works of Jaffe et al. (2), Lewis et al. (4), Gimbrone et al. (1) and Slater et al. (6). Thus at present it seems hardly possible to argue against the use of studying the morphology and biology of vessel-wall-cells grown in vitro.