Dendrimers are well-defined, highly branched, synthetic three-dimensional molecules with a large number of reactive end groups. PAMAM dendrimers form stable complexes with DNA chemistries and constitute an important class of nonviral, cationic vectors in gene delivery. The aim of this study is to examine the interactions of a 12 bp DNA oligonucletide with PAMAM-G2 and mPEG-b-PAMAM-G3 having eight surface amine groups under physiological conditions, using constant DNA concentration but varying dendrimer concentration. 1D P-31 NMR, 2D NOESY, and CD spectroscopic methods were employed to investigate the interactions between the dendrimer and the DNA. The CD experiments carried out with a constant DNA concentration of 25 mu M and dendrimer concentrations from 0 to 100 mu M indicated minimal change to the chirality of the DNA for both types of dendrimers. While the PAMAM-G2 dendrimer caused aggregation of the majority of the DNA, the 2D NMR data of the DNA with an mPEG-b-PAMAM-G3 dendrimer indicated general broadening of the 1D P-31 peaks from the DNA phosphates, a small number of H-1 chemical shift perturbations (CSPs), and reduction of specific H-1-H-1 NOE intensities. These data suggest there is minimal structural alteration of the DNA in the complex and indicate preferential binding of the dendrimer to the central AATT region of the DNA sequence. The results herein are the first such results demonstrating a soluble DNA complex with the mPEG-b-PAMAM-G3 dendrimer analyzed by multidimensional NMR.