Cholesterol efflux is the first step of reverse cholesterol transport, that protects peripheral cells from excess cholesterol accumulation. Efflux can occur by passive and SR-BI-facilitated diffusion; ABCA1 and ABCG1 mediated processes. Berberine (BBR), a cholesterol-lowering alkaloid, has several antiatherosclerotic properties; however, it was also shown to promote foam cell formation. Aim: to evaluate the effect of BBR on intracellular cholesterol metabolism, focusing on ABCA1 and ABCG1-cholesterol efflux in mouse peritoneal macrophages (MPM). Methods: MPM were labeled  with ³H-free cholesterol (FC) for 24h and successively incubated overnight in 0.2% BSA-medium with 50µg/ml of acetylated LDL (acLDL) or LXR-RXR agonists (22-OH cholesterol 5µg/ml 9cis-retinoic acid 10 µM), in the absence or presence of BBR 1µM. Efflux was promoted to Apo A-I 10µg/ml or HDL_2.. The experiments were performed either in the absence or presence of 2µg/ml of an ACAT inhibitor. Efflux was calculated as a percentage of radioactivity released in the medium over the total radioactivity incorporated by cells. A separate set of cell monolayer were extracted with isopropanol and free cholesterol (FC) and cholesteryl ester (CE) were separated by TLC. Intracellular cholesterol content was measured by a fluorimetric assay. Results: in acLDL-loaded MPM, BBR 1µM reduced ABCA1-cholesterol efflux to apoA-I by 51% ± 9.2, whereas ABCG1 efflux to HDL₂  was reduced by about 100%. BBR did not affect cholesterol uptake (88.31 ± 7.64 µg/mg protein versus 91.41 ± 3.25 µg/mg protein without or with BBR respectively). As measured by TLC, the percentage of intracellular ester (CE) was unchanged after BBR treatment (47.89% ± 3.41 versus 45.9% ± 2.53 without or with BBR respectively). This was confirmed by the observation that BBR had an inhibitory effect on ABCA1- efflux to apoA-I (55% ± 1.4) also in the presence of an ACAT inhibitor. In LXR-RXR treated MPM, the inhibitory effect of BBR 1µM was more modest either on ABCA1-efflux to Apo A-I (22% ± 6.4), and on ABCG1-efflux to HDL₂ (63% ± 9.9). Conclusions: BBR reduced ABCA1 and ABCG1-efflux in acLDL-loaded MPM, without affecting cholesterol uptake and percentage of CE. In LXR-RXR-treated MPM, the inhibitory effect of BBR was more modest. Our preliminary results suggested that BBR, despite its cholesterol-lowering effect may have a potential pro-atherosclerotic activity reducing both ABCA1 and ABCG1-efflux.