Abstract: Objective: Placenta human choriocarcinoma JEG-3 cells were used to study the possibility that pituitary growth hormone (GH) and insulin-like growth factor type I (IGF-I) act on first trimestr of pregnancy progesterone (P4) and human chorionic gonadotropin (hCG) secretion, cell proliferation and apoptosis. Material and Methods: The JEG-3 cell line was cultured in DMEM without phenol red containing 10% FBS. The cells were plated in 96-well plates at the density of 3 x103 for 24 h and treated with 10, 50, 100, or 200 ng/ml of GH or 10, 30, 100, or 250 ng/ml of IGF-I for 24 h. At the end of the culture period, cell proliferation was measured using the BrdU colorimetric assay and caspase-3 activity, as a marker of apoptosis, was determined by the colorimetric method. Media were frozen for hormone analysis by enzyme immunoassay (EIA). Results: We found that the stimulatory activities of GH and IGF-I on both P4 and hCG secretion paralleled the stimulation of cell proliferation and inhibition of apoptosis. Conclusion: Our findings suggest an important role for pituitary GH and IGF-I in normal placental function during the first trimester of pregnancy.