Rats with mammary cancer were imaged by scintigraphy: 10 rats with 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) and 10 rats with [18F]F-D-galactose. The uptake of both tracers was similar in the tumors--the tumor-to-normal tissue ratio was 2.7 +/- 1.1 for [18F]FDG and 2.3 +/- 0.9 for [18F]FDGal at 120 min after injection. In addition to the tumors [18F]FDG accumulated in the brain, bladder and heart, [18F]FDGal in the brain, bladder and liver. [18F]FDGal may be useful for tumor imaging in man; further studies should be addressed to elucidate the mechanism of [18F]FDGal uptake into tumors.