Human (h) placenta-derived choriocarcinoma cell lines (BeWo, JAR, and JEG-3) were examined for expression of pituitary GH (hGH-N) as well as placental GH variant (hGH-V) and chorionic somatomammotropin (hCS, encoded by the hCS-A or hCS-B gene). RNA was isolated and assessed using hGH-N complementary DNA since hGH and hCS genes share more than 90% sequences similarity. The relative expression is BeWo greater than JAR greater than JEG-3. In BeWo cells expression of placental hCS-A, hCS-B, and hGH-V genes, but not pituitary hGH-N, is observed using polyadenylated RNA and oligonucleotide probes specific for the different family members. The absence of hGH-N expression in BeWo cells is not due to deletion or gross rearrangement of the gene. No difference was seen between the hGH/hCS genes in genomic DNA from these cells and the DNA from placenta and pituitary when analyzed by restriction digestion and blotting. Treatment of BeWo cells with 10 nM T3 results in a 6-fold increase in messenger RNA from placental members of the hGH gene family. Levels of hCS-A, hCS-B, and hGH-V transcripts are all elevated. Cellular and secreted proteins from BeWo cells were analyzed by Western blotting, and a band of about 22 kilodaltons was detected using a polyclonal antibody which cross-reacts with hGH-V and hCS. The level of 22 kilodalton band in samples of cellular as well as released protein was increased by T3 treatment. BeWo cells provide a model system for studying hGH-V and hCS regulation as well as tissue-specific expression.