Effects of 96 h aflatoxin B1 (AFB1) exposure at concentrations from 0.2 μM to 6 μM on the mRNA and protein expression levels of the following transporters ABCB1/B4, ABCC1, ABCC2, ABCG2, OAT4 and the mRNA expression of steroid-metabolizing enzymes CYP1A1, CYP19A1, HSD3B1 and HSD17B1, and conjugating enzyme family UGT1A were evaluated in trophoblastic JEG-3 cells. Statistically significant dose-dependent five-fold increases in the expression levels with ABCC2 and OAT4 were recorded at 2 and 6μM AFB1. Protein expression of ABCG2 was decreased dose-dependently with 0.2-6 μM AFB1. With the other transporters, only a trend of increased expression was observed. Analogously, a three-fold increase in the expressions of CYP19A1, HSD3B1, HSD17B1 and UGT1A-family were observed at 0.3 μM AFB1. When an inhibitor of CYP19A1, finrozole, was dosed simultaneously with AFB1, no increases in the transcripts of transporters or steroid hydroxylases or CYP19A1 were observed. This delayed increase in the expression levels - only after 96h incubations - may indicate that the response is due to a secondary metabolite of AFB1 or other secondary controlling cascades rather than the parent compound itself. In conclusion, AFB1 affected the placental steroid synthesizing, metabolizing and conjugating enzymes as well as the expression levels of several transporter proteins in JEG-3 cells. These alterations may lead to anomalies in the foetoplacental hormonal homeostasis.