The indirect fluorescent antibody procedure was used to study the reaction of antibody, active against human connective tissue, with living and dead HeLa cells. These antibodies were fixed only at the cell surface of viable HeLa cells and were able to react with intracellular cytoplasmic components only in killed cells. Antiserums to human fibrinogen and human γ-globulin did not give this type of fixation. Components taken up by the cell from the culture medium were demonstrable in the cytoplasm of killed cells.