A computer-controlled flow resistance (CCR), to be used in a computer-controlled lung model, is presented. Flow is forced through a slit between a cylinder and a sleeve around the cylinder. The resulting flow resistance depends on the width, circumferences and the variable length of the slit. The variation in the length is computer-controlled by the position of the sleeve with respect to the cylinder. The total flow resistance also depends on inlet and outlet resistance at both sides of the slit and on flow. The dependence on flow is primarily due to the shape of the inlet of the slit. The resistance of the slit itself is almost independent of flow. The resistance is calculated during a calibration phase at different positions of the sleeve, for flow values from 0.05 to 1.0 litre.s-1 (inflow) and from -0.05 to -1.0 litre.s-1 (outflow). To simulate a required resistance pattern, as, for instance, will occur during breathing, at each moment the set position of the sleeve is calculated by means of an interpolation from the relationship between flow resistance and position of the sleeve. The internal diameter of the sleeve is fixed. To tune the resistance range for a specific simulation, the cylinder is changed for one with different diameter, changing the width of the slit.