A lipoid based contrast material containing 53% of ethiodized oil in emulsion form was developed for computed tomography (CT) of the liver and spleen and tested in rabbits and monkeys. An i.v. dose of 0.2 ml/kg selectively opacified the liver and spleen, resulting in an average increase of 23 EMI units (500 scale) in the attenuation of the liver and a higher increase in the attenuation of the spleen. When injected into rhesus monkeys with carcinogen-induced hepatomas there was a significant improvement in the visualization of the tumor, and small lesions, undetectable on the preliminary CT scan, became visible. Toxicity studies are in progress.