The growth of the aggregates of the dihydroxylated bile salt sodium taurodeoxycholate (NaTDC) upon NaCl addition and the involvement of the counterion were investigated by NMR spectroscopy of monoatomic ionic species. Na-23 T-1 values from 0.015, 0.100, and 0.200 mol kg(-1) NaTDC solutions in D2O, at variable NaCl content, proved to be sensitive to the transition from primary to secondary aggregates, which occurs in the former sample, and to intermicellar interaction. Some Br-79 NMR measurements were performed on a 0.100 mol kg(-1) NaTDC sample added by NaBr in place of NaCl for comparison purposes. The Na-23, Cl-35, and Cl-37 double quantum filtered (DQF) patterns, from the 0.100 mol kg(-1) NaTDC sample, and Na-23 ones also from the 0.200 mol kg(-1) NaTDC one, in the presence of 0.750 mol kg(-1) NaCl, are a clear manifestation of motional anisotropy. Moreover, the DQF spectra of Na-23 and Cl-37, which possess close quadrupole moments, display a striking similarity. The DQF lineshapes were simulated exploiting the Sci-lab environment to obtain an estimate of the residual quadrupole splitting magnitude. These results support the description of NaTDC micelles as cylindrical aggregates, strongly interacting at high ionic strengths, and capable of association with added electrolytes. (c) 2012 Elsevier Inc. All rights reserved.