4-nonylphenol (4-NP) is an estrogenic endocrine active chemical that is present in detergents and is known to contaminate food and drinking water. The aim of the present study was to evaluate whether 4-NP crosses the human placenta and if so, to what extent. Human placentae obtained from healthy term singleton pregnancies were utilized in a dual ex-vivo re-circulating model of placental perfusion. Six placentae were perfused for 180 min following addition of 4-NP (30 ng/mL) to the maternal perfusate. Antipyrine and FITC dextran were used as positive and negative controls respectively to validate the integrity of the circuits. 4-NP was measured by High Performance Liquid Chromatography coupled with Fluorescence Detection (HPLC-FD). After 180 min of perfusion the transfer percentages for antipyrine and 4-NP were 25.6 ± 1.4% (mean ± s.e.m, n = 6) and 22.75 ± 3.76% respectively and the transfer index for 4-NP was 0.8. We conclude that the intact form of 4-NP at environmentally relevant concentrations can transfer across the human placenta albeit at a slow rate.