Floating gallstones in bile without added contrast material.

Floating gallstones can occur without the administration of contrast material to increase the specific gravity of bile. This was observed in three patients in 17 months. After a long fast, a large stone was noticed to float because of the high specific gravity of inspissated bile. This stone sank after the patient resumed food intake. In another patient, some stones floated while others sank due to their difference in specific gravity. Sonographic demonstration of a floating stone, however, requires certain strict criteria.