The effect of adding acetylated poly(propyleneimine) dendrimers to the structure and rheology of aqueous solutions of high molecular weight poly(ethylene oxide) (PEO) was investigated by rheology and small-angle neutron scattering in a temperature range of 10-40 degrees C. In the semidilute regime, the steady shear rheology of PEO solutions was unmodified by the addition of dendrimers at a comparable weight concentration. At the highest concentrations studied, the addition of acetylated dendrimers suppressed the onset of a low-frequency elastic modulus at the lowest temperature investigated. For comparison, the addition of PEO of a comparable molecular weight at the same weight fr action resulted in a milder suppression but, unlike the dendrimers, greatly increased the solution viscosity. The addition of acetylated dendrimers to a semidilute PEO solution at 10 degrees C substantially reduced the solution turbidity. These effects on the rheology and optical properties were confirmed by small-angle neutron scattering measurements of the molecular structure of the mixture. Additional SANS measurements in the dilute regime (0.1 wt % PEG) showed quantitatively that the dendrimers decorated the PEO chains in a necklace structure, such as that observed previously for micelles. The results suggested a mechanism of rheology modification whereby the dendrimers disrupted the association network structure in the PEO solution at lower temperatures by preferentially associating with the PEO chains in solution.