Gd-Ti monotectic alloys were studied in a wide temperature range by the sessile drop technique. The eutectic and monotectic transformations in Gd-Ti alloys upon heating were in situ monitored by a high-speed and high-resolution CCD camera. Our findings suggest that the existing Gd-Ti phase diagram significantly underestimates the monotectic and binodal temperatures in this system. The wetting behavior and the high-temperature interaction of the Gd-Ti melts with yttria and yttria-stabilized zirconia substrates were investigated.