The first experimental measurements of surface slip using a torsional ultrasonic oscillator have been carried out. Slip was measured at the interface between water and a roughened fused quartz surface coated with a hydrophobic fluoropolymer surfactant. The magnitude of the slip length b was calculated to be 50 nm for 40 kHz oscillations at shear rates ranging from 500 to 3500 s(-1). This value is broadly in agreement with comparable data in the literature. Reliable quantitative measurements of this type are important for effective study of the surface slip mechanism for Newtonian fluids. (C) 2007 Elsevier B.V. All rights reserved.