The presence of choriogonadotropin- and alpha-subunit-like materials in two species of bacteria identified as Staphylococcus simulans and Streptococcus faecalis have been demonstrated by the indirect fluorescein-labeled and the indirect peroxidase-labeled immunocytochemical techniques, utilizing antiserum for human choriogonadotropin, for its alpha and beta-subunits and the bera-subunit COOH-terminal peptide. The bacteria were originally isolated from the urine of two patients with advanced forms of cancer. Chromatography done on the water-soluble extract of acetone powder preparations of the bacterial cultures revealed the presence of a material similar to the complete trophoblastic hormone and to its beta-subunit in the culture media of S. simulans, and to the beta-subunit in the media of S. faecalis. No free alpha-subunit was detectable. Furthermore, the choriogonadotropin-like factor demonstrated biological activity in in vivo assay systems. From the present results, it can be concluded that some species of "cancer-associated" bacteria can synthesize a human trophoblastic hormone-like glycoprotein with physicochemical properties similar to those of the human trophoblastic hormone that is biologically active and that is either released complete or as one of its subunits in the culture media.