A new continuous emulsification process has been developed that is capable of generating very uniform droplets in a single stage process. It is based on thread break-up in the lumen of hollow fibre membranes, whose material is selected to be preferentially wetted by the continuous phase of the emulsion to be produced. This phase is pressed from the outside through the fibre wall, while the phase to be dispersed enters the hollow fibre through one of the lumen openings. It is disconnected from the fibre wall by a film of permeating continuous phase inducing instabilities in the inner phase. After break-up, a two-phase train of equally spaced droplets leaves the other lumen end into a product receiver. The emulsion thus generated shows an extremely narrow droplet size distribution and can be produced without emulsifiers. Its mean size is directly correlated with the inner diameter of the fibres, a fact that limits its range to values between 300 and 2000 mu m. The process has the potential of being very cost efficient as it consumes little energy and does not require complex equipment. Four different membranes and a wide range of fluid properties, i.e. viscosity, density and interfacial tension were studied. The purpose of these experiments was an analysis of the droplet diameter and its distribution upon physical properties and operating parameters. The system can be operated very stably within a wide range of fluid and process parameters. Next steps are an investigation of applications and the development of a fluid dynamic model. (c) 2007 Elsevier B.V. All rights reserved.