Slip flow occurs in colloidal crystals made of 470 nm silica spheres that are chemically modified with hydrocarbon, giving enhanced volume flow rates and a narrower distribution of fluid velocities. Bovine serum albumin separates by pressure-driven flow with a zone that is 15-fold narrower than the theoretical limit for Hagen-Poiseuille flow. The zone variance, normalized for separation length, is 15 nm, which is 500-fold smaller than previous reports for pressure-driven protein chromatography. A colloidal crystal is shown to separate a monoclonal antibody from its aggregates in only 40 s, representing a 10-fold increase in speed. Slip flow, thus, has profound implications for protein chromatography.