The aim of this study is to develop an experimental method which provides relevant data about the rheological behavior of polymer melts in pressure-driven flows in microscale geometries. In order to get better description of the physics involved in such flows, numerical simulation with commercial and in-house softwares was implemented, especially with molecular dynamics constitutive models. Thus, a modular rheometrical slit die equipped with pressure and temperature transducers was designed and adapted to a capillary rheometer. Different gap dimensions between 50 mu m and 200 mu m are available. The measurements were performed with high density polyethylene and low density polyethylene. The device was assessed by comparing to usual rheometers. The wall slip was investigated according to Mooney's method. Simulations were conducted with MATLAB (R) by implementing the Doi-Edwards' tube model and the molecular stress function of Wagner to take into account the enhanced orientation of the molecules due to the very close vicinity of the die walls. The flow was also simulated with POLYFLOW (R). The pressure effect on the geometry and on the polymer material was investigated. Experimental results were compared to calculations in terms of pressure values. The conclusions somewhat modify the prospects for future studies of such flows. (C) 2014 The Society of Rheology.