A new Micro-(p, V, T) apparatus, based on the piston-in-a-bottle design, has been developed for measurement of liquid densities at pressures up to 500 MPa. The temperature range corresponding to complete immersion of the cell in the thermostat fluid is from T = 263 K to T = 333 K. Friction problems are overcome by having a rotating piston, with varying rotational speeds available. The sample size is about 0.8 cm(3). Results for freezing pressure are reported for (n-hexane + n-hexadecane). Calculation of the effects of an increase in pressure and change in temperature on the components of the cell leads to the determination of liquid densities at pressures up to 500 MPa which agree within +/-1.5 per cent with reliable literature values. This can be improved to better than +/-0.4 per cent by calibration, as is demonstrated by comparison of measured densities for n-octane with bellows volumometer data.