Two techniques have been developed for the measurement of the infrared absorption of glasses at room temperature and of their melts up to 1000°C. In a vertical film apparatus, dehydration and the control of sample thickness may be carried out simultaneously. At high temperatures, the breakage of the film through flow is circumvented by a horizontal film arrangement. By the formation of suitable thin filmsin situ, rapid absorption of water is prevented. These methods are thus particularly suitable for highly hygroscopic materials where the conventional KBr disk technique is unsatisfactory. The advantages of the two techniques are demonstrated by measurements carried out on glassy and liquid B2O3up to 1000°C.