Infrared sensitization of photographic emulsion response to visible light is a useful technique for visualizing IR laser beams. In this work, it is demonstrated that this sensitization results from heating by the IR beam. Investigation of the dependence of sensitization by pulsed CO(2) laser (10.6-microm) preexposures on visible background density, IR fluence, visible wavelength, delay between exposures, and spatial frequency are described. Infrared fluences as low as 10 mJ/cm(2), a dynamic range greater than 100, and a resolution better than 50 lines/mm were observed. Suggestions for further improvements of the technique are made.