Water-soluble Gd3+-cored poly(ether amide) dendrimer complexes, bearing a diethylenetriaminepentaacetic acid Gd3+ complex (GdDTPA) core, were synthesized. The longitudinal proton relaxivity (R-1), governed mainly by the rotation correlation time of the paramagnetic Gd3+ center, was measured in water (37 degreesC, 20 MHz). An anchor effect at the focal point of the hydrophilic dendrimer was experimentally evaluated for the first time, through a comparison of the R-1 values with the ones reported for various Gd3+ complexes, including linear copolymers of GdDTPA linked by various lengths of aliphatic chains via amide bonds. Unusually large R-1 values for the first- and second-generation Gd3+-cored dendrimer complexes (6.1 and 9.3 mM(-1) s(-1), respectively), even with relatively low molecular weights (1355 and 3877, respectively), suggested a remarkable increase in the local rigidity around the GdDTPA core. The internal rigidity of the dendrimer was supposed to take advantage of the increased nominal molecular weight in water via multihydration to the dendron to increase the rotation correlation time, and this resulted in the observed R-1 gain. (C) 2004 Wiley Periodicals, Inc.