Graphic representation of samples (A) with simultaneous activity of both Pgp and MRP1 (6 patients; 15%); (B) with MRP1 activity, without activity of Pgp (5 patients; 12.5%); (C) with Pgp activity, without activity of MRP1 (7 patients; 17.5%); and (D) without activity of both Pgp and MRP1 (22 patients; 55%). The area included between the two horizontal bold lines represents the samples with a negative activity of Pgp (fluorescence ratios of samples which ranged between 0.61 and 1.39 represent experimental variability). The area included between the two vertical dotted lines represented the samples without activity of MRP1 (fluorescence ratios of samples which ranged between 0.72 and 1.28 represent experimental variability). There was a weak correlation (r = .39, P = .008) between MRP1 and Pgp activity. *Two samples.