The performance of microbore columns with polypropylene (PP) capillary-channeled polymer (C-CP) fibers as the support/stationary phase for separation of macromolecules has been investigated. Polypropylene C-CP fibers (40 μm diameter) were packed in fluorinated ethylene propylene (FEP) tubing of inner diameter 0.8 mm and lengths of 40, 60, 80, and 110 cm. The performance of PP fiber packed microbore columns (peak width, peak capacity, and resolution) was evaluated for separation of a three-protein mixture of ribonuclease A, cytochrome c, and transferrin under reversed-phase gradient conditions. The low backpressure characteristics of C-CP fiber columns enable operation at high linear velocities (up to 75 mm s(-1) at 1.5 mL min(-1)). In contrast with the performance of other phases, such velocities enable enhanced resolution of the three-protein mixture, because peak widths decrease with velocity. Increased column length resulted in increased resolution, because the peak widths remained essentially constant, although retention times increased. In addition, it was found that the peak capacity increased with column length and linear velocity. Radial compression of the microbore tubing enhanced the homogeneity of the packing and, thereby, separation efficiency and resolution. Radial compression of columns resulted in a decrease in the interstitial fraction (~5%), but increased resolution of ~14% between ribonuclease A and cytochrome c. Even so, a linear velocity of 75 mm s(-1) required a backpressure of 9.5 MPa only. It is clear that the fluid and solute-transport properties of the C-CP fiber microbore columns afford far better performance than is obtainable by use of standard format columns. The ability to achieve high separation efficiencies, rapidly and with low volume flow rates, holds promise for high-capacity protein separations in proteomics applications.