In this study sequential 1H and 19F magnetic resonance imaging methods were used to map the distribution of fluorinated compounds in vivo. An intravenously administered emulsion of perfluorooctylbromide (PFOB), an agent known to localize in the reticuloendothelial system, was detected in the liver and spleen of all studied hamsters and mice using 19F MRI. Lungs and salivary glands were also affected in some animals. Using a G. E. NMR CSI 2-T spectroscopy/imaging system, projection 19F images were obtained in 4 to 8 min. Subsequent mouse studies using a thick-slice driven equilibrium pulse sequence produced 19F images with an improved signal-to-noise ratio in a shorter acquisition time. With PFOB, 19F MRI has the capability of detecting macrophages in the reticuloendothelial system and in other sites where macrophages congregate. This is the first report where the reticuloendothelial system was specifically imaged in live animals and where driven equilibrium imaging techniques have been applied to 19F MRI. © Academic Press, Inc.