Portable x-ray fluorescence technology has proved to be a very useful tool for identifying the mineral constituents of rock art paintings. This paper describes its use to identify chromium, whose likely source was the mineral fuchsite, as the green coloring agent in Montana and Wyoming pictographs. High levels of lead were also detected in a series of pictographs from Weatherman Draw in south central Montana that were reported to have been repainted or retouched to enhance their visibility.