We present a comprehensive experimental study of homogeneous bubble nucleation in rhyolitic magmas. It was undertaken by performing a series of isothermal (800 ¿C) rapid decompression experiments using crystal-free rhyolitic liquids containing from 4 to 7 wt% H2O and various CO2 contents of up to 820 ppm. No homogeneous nucleation was observed in samples containing 4.5 wt% H2O and 150--200 MPa), and that the pressure of homogeneous nucleation will be strongly sensitive to the multicomponent volatile composition of the liquid. ¿ 1999 American Geophysical Union