The potency of benzo[a]pyrene (BaP), anthracene, 7-methylbenzo-[a]-pyrene and liquid n-paraffin mix towards the aryl hydrocarbon receptor (AhR) was tested by using the chemical-activated luciferase expression (CALUX) bioassay. The H1L7.5c1 cell line was exposed to different (dilution) doses of the tested chemicals, and for different exposure times (2.5 and 24 hours). BaP and 2,3,7,8 TCDD were used as reference ligands for both the 2.5 and 24 exposure times. Strong induction and clear dose-response curves were obtained for BaP, anthracene and 7-methylbenzo-a-pyrene under 2.5h exposure time. The n-Paraffin mix did not give any response whatever the exposure time considered. In addition, the dose-response curve of 7-methylbenzo-[a]-pyrene was close to that observed for BaP for an exposure time of 2.5 h. The potencies, calculated based on 20%,50% and 80% effective concentrations of 7-methylbenzo-[a]-pyrene and anthracene were found to be approximately twice and 0.01 times the reference BaP for a 2.5h exposure time. However, these potencies are both 10 million times lower than the TCDD reference for a 24h exposure time. By contrast, the BaP potency under 24h exposure time was around 100 times lower than the potency of the TCDD reference. This study showed also that the methylated polycyclic aromatic hydrocarbons (PAHs) are more persistent (less degraded) than the traditional PAHs over short exposure times.