The synthesis of pregnancy-specific beta 1-glycoprotein (PS beta G) was studied in simian virus 40 temperature-sensitive A mutant-transformed human first trimester and term placental cells. At the permissive temperature (33 C, transformed phenotype), they produced low levels of PS beta G. At the restrictive temperature (40 C), the transformed phenotype was lost, and the production of PS beta G was greatly enhanced. The PS beta G produced by these transformed placental cells resembled the purified placental PS beta G by several criteria. Both cell and placental PS beta G bound to Concanavalin A-Sepharose and were, therefore, glycoproteins. The cell PS beta G cochromatographed with placental PS beta G on a Bio-Gel A-0.5m column. Furthermore, the slopes of the dose-response curves for the cell PS beta G were indistinguishable from that for placental PS beta G. The synthesis of PS beta G at both 33 and 40 C in these placental cells was greatly induced by sodium butyrate and 5-bromo-2'-deoxyuridine. Sodium butyrate was a more effective inducer at 33 C, whereas BrdUrd appeared to be a better inducer at 40 C.