We report that a rapid drop of pressure applied to a melt whose crystallization point is a decreasing function of the pressure may, if the temperature, the initial pressure, and the final pressure are appropriately chosen, be equivalent to a rapid thermal quenching. In particular, it may lead to the formation of metastable crystalline or glassy phases bulk materials. The method might be useful to simulate adiabatic decompressions subsequent to shocks such as meteorite impacts. The relation between the undercooling rate(&ngr;c)obtained by rapid decompression and the rate of pressure release(&ngr;p)is given by&ngr;c=k&ngr;p,wherekis the drop rate of the melting point with pressure. This method is evaluated for the Al–Ge system. The solidification products are either stable or metastable crystalline compounds, depending on the rate at which the pressure is released. Our experimental results indicate that quenching with rapid decompression is an effective method to generate high undercooling rates exceeding105 Ks−1.©1997 American Institute of Physics.