P-glycoprotein is one of the best studied transmembranar proteins directly related with multidrug resistance phenomenon. Using a refined P-gp structure recently published by our group, new docking studies have identified three distinct binding sites: two for substrates (H- and R-sites) and one for modulators (Modulator-site), which are in perfect agreement with experimental studies described in literature. From these docking studies, it was observed that the acylation pattern at the pentacyclic ring of lathyrane-type macrocyclic diterpenes influences the affinity towards the Modulator-site.