In this study, we investigated the binding of DNA with poly(ethylene glycol) (PEG) of different sizes and compositions such as PEG 3350, PEG 6000, and mPEG-anthracene in aqueous solution at physiological conditions. The effects of size and composition on DNA aggregation and condensation as well as conformation were determined using Fourier transform infrared (FTIR), UV-visible, CD, fluorescence spectroscopic methods and atomic force microscopy (AFM). Structural analysis showed moderate complex formation for PEG 3350 and PEG 6000 and weaker interaction for mPE-anthracene-DNA adducts with both hydrophilic and hydrophobic contacts. The order of +/- stability of the complexes formed is K(PEG) (6000) = 1.5 (+/- 0.4) x 10(4) M(-1) > K(PEG 3350) = 7.9 (+/- 1) x 10(3) M(-1) > K(mPEG-anthracene) = 3.6 (+/- 0.8) x 10(3) M(-1) with nearly 1 bound PEG molecule per DNA. No B-DNA conformational changes were observed, while DNA condensation and particle formation occurred at high PEG concentration.