Our experience on the use, for several years, of an off line data processing system, has permitted the development of a more advanced system. The basis of the new system is implantation in the laboratory of a minicomputer, linked secondarily to a large computer. The introduction of viewing apparatus favours the development of conversational procedures essential for this application. The organisation of work stands, which varies with the type of blood investigation carried out, whether automatic, semi-automatic or manual, and depends on the use of specialised terminal, e.g. key-board, screen or printing machine, was particularly studied. Simpler procedures were also fully studied, for a routine laboratory must continue to function if the computer breaks down.