Agonist profiles for each receptor were determined by cotransfection of expression vectors for mouse (Kliewer et al., 1998; Lehmann et al., 1998), rat (Savas et al., 1999), rabbit (Savas et al., 1999), or human (Bertilsson et al., 1998; Blumberg et al., 1998; Lehmann et al., 1998) PXR with either a DR-3 or ER-6 reporter construct. Because different reporter constructs and different cell lines were used in these transfection assays, only qualitative descriptions are used to compare the responses: strong activator, ++; modest activator, +; and not efficacious, –.