Sodium cyclamate was suspended in cholesterol pellets that were surgically implanted in the urinary bladders of mice. In duplicate experiments, incidences of mouse bladder carcinomas observed in animals exposed to these pellets were 78 and 61 percent compared with incidences of 13 and 12 percent in control mice exposed to pellets of pure cholesterol. The exposure of the mouse bladder to sodium cyclamate was very brief, as the time required for 50 percent of the compound to disappear from the pellets was about 1 hour. This experimental technique was found to be highly sensitive, reproducible, and predictive of the bladder carcinogenicity of orally administered cyclamate.