We established an in situ and simultaneous measurement system for solute distribution and temperature distribution in high-temperature solutions. The system consists of an infrared camera, an X-ray fluorescence spectrometer for concentration measurement and a sample stage with a two-zone heater. A sample holder is composed of some graphite parts with a quartz glass window at the bottom of holder for monitoring the infrared image. Concentration measurements are performed by the X-ray analysis through the graphite lid at the top of the holder. The present system was applied to the in situ measurement of the solute and temperature distributions in the gallium-zinc solution during the crystal growth by the solute supplied zone melting method. We selected the thin sample with the thickness of 500 pm to observe the solute distribution characterized by diffusion process. As a result, we successfully observed the process in which the solute distribution changed and consequently reached the stationary state due to the diffusion in the linear temperature gradient. These results show that the present system can be a powerful tool for actual survey of supercooling and supersaturation. (C) 2002 Elsevier Science B.V. All rights reserved.