Determination of the particle size and zeta potential of emulsions formed by high-pressure homogenisation has been made by electro acoustics using a flow-through version of an AcoustoSizer. The sunflower oil-in-water emulsions were formed by passing the stirred oil-water mixture through a homogeniser in the presence of sodium dodecyl sulfate (SDS) at natural pH (6-7). The number of passages, the passing temperature and the volume fraction of oil are major factors influencing the final particle size, while the zeta potential is only slightly affected. The electroacoustic technique makes it possible to measure directly the size and zeta potential of the emulsion droplets from 2 to 50% oil volume fraction. The zeta potential was similar to -95 mV and the median particle size, measured after 15 passages, decreased from 0.76 mum (2% v/v) to 0.23 mum (50% v/v) at 30 degreesC.