Whilst there are numerous experimental, theoretical and computational studies of Taylor flow in microchannels, the intermittent slugannular regime has largely been neglected. In this paper time-resolved micro-PIV data are collected and used to study the flow characteristics of a gasliquid system for flow regimes spanning Taylor to annular flow. The experimental work used a 1.73 mm diameter channel with water and nitrogen as the working fluids, for gas and liquid superficial velocity ranges of 0.358.65 m s(-1) (40 < Re-G < 1000) and 0.0710.18 m s(-1) (120 < Re-L < 300), respectively. Time-averaged velocity profiles were obtained in the liquid film surrounding the gas bubbles (or the gas core in the pseudo-annular flow regime) and in the liquid slugs (which changed from regular slugs to annular rings as the gas superficial velocity was increased). These data showed that the velocity in the liquid film relaxed back to an equilibrium value following the passage of each liquid slug or annular ring. In contrast rather flat velocity profiles were observed in the liquid slug. Based on a simple representation of the flow structure, average gas holdups were estimated using independent experimental data obtained by the micro-PIV technique and by direct observation of the flow structure. A phenomenological model of intermittent slug flow, based on the representation of the flow structure as a train of slugs and bubbles moving over a liquid film, is used to interpret the experimental data. The modelling work highlights the different behaviour of the limiting cases of slug and annular flow, in terms of the gasliquid interfacial shear and its influence on the pressure field. (C) 2010 Elsevier Ltd. All rights reserved.