High-pressure homogenisation is a key unit operation used to disrupt fat globules or cells containing intracellular bioproducts (AlChE J. 43(4) (1997) 1100). Modelling and optimisation of a small homogenising unit are often restrained by a lack of information on the flow conditions within the homogeniser valve. A numerical investigation of the flow within such a new homogenising valve, capable to reach pressure as high as 350 MPa (Stansted Fluid Power Ltd, UK) is presented. Results are obtained using the finite-volume technique and a RNG kappa-epsilon turbulence model with low Reynolds number near wall treatment conditions. An experimental measurement of the size of the valve gap is presented in order to validate mathematical relations that give valve gap sizes versus homogenising pressure. The modelling results give detailed information on the mechanical stresses and the high shear rates in small disruption valves, and also reveal other phenomena that could not be easily determined experimentally. (C) 2003 Elsevier Ltd. All rights reserved.