BCRP / ABCG2 is a key determinant of pharmacokinetics of substrate drugs. Several BCRP substrates and inhibitors are of low passive permeability, and the vesicular transport assay works well in this permeability space. Membranes were prepared from BCRP-HEK293, MCF-7/MX, and baculovirus-infected Sf9 cells with (BCRP-Sf9-HAM), and without (BCRP-Sf9) cholesterol loading. K values for three substrates - estrone-3-sulfate, sulfasalazine, topotecan - correlated well between the four expression systems. In contrast, a 10-20-fold range in V values was observed, with BCRP-HEK293 membranes possessing the largest dynamic range. IC values of the different test systems were similar to each other, with 94.4% of pairwise comparisons being within 3-fold. Substrate dependent inhibition showed somewhat greater variation, as 81.4% of IC values in the BCRP-HEK293 membranes were within 3-fold in pairwise comparisons. Overall, BCRP-HEK293 membranes demonstrated the highest activity. The IC values showed good concordance but substrate dependent inhibition was observed for some drugs.