A study of the alterations in the structure of turbulence due to the presence of PEO 301 dilute solutions was made using two experimental techniques. A photographic method was used to explore the wall region from 0.05 to 1 mm of the wall1and laser Doppler anemometry in the core and the buffer layer.2It was shown that, even if the velocities are reduced in the vicinity of the wall (in correlation with the fluid characteristics), the reduced coordinate profile remains unchanged in the laminar sublayer (y+<5). With very low concentrations (∼5 ppm) the mean velocity profile is not strongly affected even if the drag reduction is more than 40%. In the core, the shift of the profile observed by several authors was confirmed. The most important effect of the macromolecules was observed in the buffer layer where both the influence of the Reynolds number and the characteristics of the fluid were noted. The change in the structure of turbulence was observed3in measuring the streamwise turbulent intensities. It was shown that the maximum is shifted far from the wall in relation to the increase in the thickness of the viscous sublayer. A spectral analysis of the longitudinal velocity fluctuations by calculation of the probability density functions, the autocorrelation functions, and the power spectrum confirmed the idea of a transfer of energy from high frequency to low frequency turbulence structures. Therefore, it appears that the mechanism of drag reduction has to be found in the change in both the turbulent energy production (increase in the great structures) and dissipation (decrease in the importance of small eddies).