Bailey, Jack S. (George Washington University, Washington, D. C.), Harold W. Clark, William R. Felts, Richard C. Fowler, and Thomas McP. Brown. Antigenic properties of pleuropneumonia-like organisms from tissue cell cultures and the human genital area. J. Bacteriol. 82:542-547. 1961.-Antigens were prepared from several tissue culture and human genital strains of pleuropneumonia-like organisms (PPLO) by a method utilizing continuous agitation of the incubating cultures. Antisera were produced in rabbits by intravenous injection of suspensions of these organisms standardized turbidimetrically. The antigenic properties of the selected strains were compared by agglutination techniques supplemented by a test based upon the inhibition of growth of PPLO by specific antisera.The majority of tissue culture strains of PPLO studied, including contaminants from several HeLa cell lines, appeared to be antigenically similar to the human type 1 strains. However, one strain (Sp-1) from a HeLa cell line was found to be related to the human type 2 PPLO.