A mass spectrometer was used to monitor the release of water from quartz samples heated to 1200°C in vacuum. Both hydrothermal quartz and granitic quartz show abundant fluid inclusion ruptures over the temperature range from 100°C to 550°C and, in most cases, a prominent water release at the quartz alpha-beta transition (573°C). Fluid inclusion ruptures above this stage are rare. High temperature water release from hydrothermal quartz is negligible, but it is greater (though more variable) for the quartz from granites. No water release can be related to the quartz-tridymite transition.