The present investigation deals with the detailed aerodynamic flow near a rotating helicopter rotor blade. Three-component velocity measurements using a Stereoscopic Particle Image Velocimetry system reveal the details of the near tip flow at various blade angle-of-attack values. The instantaneous flow in selected planes that are almost normal to the rotor blade tips is measured in a phaselocked manner as observed from the stationary frame. A model helicopter with a two-bladed rotor is utilized for experiments at a speed of 570 rpm corresponding to a tip velocity of 35.8 m/s (117.5 ft/s) and a tip Reynolds number of 9.6 x 104. Radial motion along the blade is analyzed with 3D PIV. Aerodynamic results obtained near the tip region, and specific issues related to the 3D PIV technique are discussed in detail. The current PIV results effectively show fine details of highly 3D flow fields near rotating machinery components.