A new, lipoid-based experimental contrast material (AG 60-99), an emulsion containing 35% iodenated ethyl esters of the fatty acids of poppy seed oil with soy lecithin, glucose, disodium phosphate, a surface active agent (polyoxyethylene glycol monostearate) and water, was infused i.v. into 29 rhesus monkeys. The injections resulted in dense hepatosplenograms preserving diagnostic quality for over 24 h and enabling routine utilization of tomography. This technique is capable of demonstrating simulated hepatic masses as small as 5 mm in diameter in vivo. Limited histopathologic and toxicity studies showed no serious or lasting toxic manifestations from AG 60-99 and none of the animals died from it. AG 60-99 is potentially useful in the radiographic detection of early metastatic or lymphomatous involvement of the liver and spleen.