A gas measurement device for measuring at least one gas in the stomach of a mammal, the device comprises a housing for being located in the mammal's stomach and providing at least one gas sensor for detecting the gas. The housing is impermeable to liquid within the stomach. The device may also comprise a controller disposed within the housing and which is electrically coupled to the at least one gas sensor. The controller is arranged to periodically process an output from the gas sensor(s) to provide data indicative of the amount of the gas within the stomach. The controller can include a wireless transmitter for transmitting the data to a remotely located receiving device disposed exterior to the mammal.